Selection of pilot pattern according to channel characteristics for a MIMO-OFDM system

(54) Title: PILOT SIGNAL TRANSMISSION TO AN ORTHOGONAL FREQUENCY WIRELESS COMMUNICATION SYSTEM (30) Unionist Priority: 27/10/2005 us 11 / 261,361 (73) Owner (s): Qualcomm Incorporated (72) Inventor (s): Alexei Gorokhov, Arak Sutivong, Ayman Fawzy Naguib, Dhananjay Ashok Gore, Tingfang Ji (74) Attorney (s): Montaury Pimenta, Machado & Lioce (86) International Request: pct us2006060336de27 / i0 / 2006 (87) Publication International: wo 2007/051 i90of 03/05/2007 (57) Summary: pilot signal transmission to an ORTHOGONAL FREQUENCY DIVISION WIRELESS COMMUNICATION SYSTEM. A plurality of transmission standards are provided for pilot systems transmitted from a mobile station or base station. Depending on the frequency selectivity and / or time selectivity of the channel between the mobile station and the base station, an appropriate pattern is selected. The selected pattern allows for improved reception of pilot symbols. In addition, scrambling codes can be applied to patterns to reduce interference and / or polarization from different mobile stations on the same frequencies and on the same partitions.

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PILOT SIGNAL TRANSMISSION TO A WIRELESS COMMUNICATION SYSTEM OF ORTHOGONAL FREQUENCY.

Field of the Invention

This document generally relates to wireless communication and, among other things, the transmission of pilot information in a wireless communication system with orthogonal frequency division.

Description of the Prior Art

An orthogonal frequency division (OFDMA) multiple access system uses orthogonal frequency division (OFDM) multiplexing. OFDM is a multi-carrier modulation technique that divides the general system bandwidth into multiple orthogonal frequency (N) subcarriers. These subcarriers can also be called tones, bands, and frequency channels. Each subcarrier can be modulated with data. Up to N modulation symbols can be sent on the N total subcarriers in each OFDM symbol period. These modulation symbols are converted into the time domain with an N-point Inverse Fast Fourier Transform (IFFT) to generate a transformed symbol that contains N samples or chips in the time domain.

In a frequency hopping communication system, data is transmitted on different frequency subcarriers at different time intervals, which can be referred to as hopping periods. These frequency subcarriers can be provided by orthogonal frequency division multiplexing, other multi-carrier modulation techniques, or some other constructions. With frequency hopping, the data transmission jumps from subcarrier to subcarrier in a pseudo-random mode. This leap provides diversity of frequency and allows data transmission to resist

2/38 better to harmful path effects like narrow band interference, blocking, fading, and so on.

An OFDMA system can support multiple mobile stations simultaneously. For a frequency hopping OFDMA system, a mobile transmission can be associated with being sent in a sequence of one data to a specific hopping channel. specific multiple period

This string use for jumping. Multiple data transmissions to mobile stations can from one station to traffic which is frequency (FH)

FH indicates the subcarrier to transmit data in each one being sent simultaneously in multiple channels associated with different FH sequences.

traffic that are

These FH sequences can be defined to be orthogonal to each other so that only one traffic channel, and thus only one data transmission, uses each subcarrier in each hopping period. By using orthogonal FH strings, multiple data transmissions generally do not interfere with each other while enjoying the benefits of frequency diversity.

An accurate estimate of a wireless channel between a transmitter and a receiver is usually needed to retrieve data sent over the wireless channel. Channel estimation is typically performed by sending a pilot from the transmitter and measuring the pilot at the receiver. The pilot signal is composed of pilot symbols that are known a priori by both the transmitter and the receiver. The receiver can thus estimate the channel response based on the received symbols and the

Part of each transmission is known symbols.

from any base station-specific mobile station, often referred to as a link broadcast

3/38 reverse, during a jump period is allocated for transmission of pilot symbols. Generally, the number of pilot symbols determines the quality of channel estimation, and consequently the performance of packet error rate. However, the use of pilot symbols causes a reduction in the effective transmission data rate that can be obtained. That is, as more bandwidth is allocated to pilot information, less bandwidth becomes available for data transmission.

One type of FH-OFDMA system is a blocked hop system where multiple mobile stations are assigned to a contiguous group of frequencies and symbol periods. In such a system, it is important that pilot information is received securely from the mobile station, while at the same time reducing the bandwidth that is allocated to pilot information, since the block has a limited amount of symbols and tones available to be used for both pilot and data transmission.

Summary of the Invention

In one embodiment, pilot symbol patterns are provided for pilot symbols transmitted from a mobile station or a base station. The standard allows for improved reception and demodulation of transmitted pilot symbols. The selection of pilot patterns can be based on a user frequency selectivity and a frequency selective limit.

In additional modalities, schemes are provided to improve the ability to multiplex pilot symbols without interference and / or polarization from different mobile stations in the same sector of a base station through the same frequencies and in the same time partitions in an OFDM system.

4/38 li 'a

In additional modalities, schemes are provided to reduce polarization or interference, in pilot symbols transmitted from different mobile stations in neighboring cells through the same frequencies and in the same time partitions in an OFDM system.

In other embodiments, methods are provided for changing pilot symbol patterns. In addition, in other additional embodiments, methods for generating pilot symbols are provided.

Brief Description of the Figures

The characteristics, nature and advantages of the present modalities can become more evident from the detailed description exposed below when taken in combination with the drawings in which similar reference characters correspond correspondingly from start to finish and in which:

Figure 1 - illustrates a multiple access wireless communication system according to a modality;

Figure 2 - illustrates a spectrum allocation scheme for a multiple access wireless communication system according to a modality;

Figure 3A - illustrates a block diagram of a pilot assignment scheme according to a modality;

Figure 3B - illustrates a block diagram of a pilot assignment scheme according to another modality;

Figures 3C-3E illustrate block diagrams of pilot assignment schemes according to additional modalities;

Figure 4A - illustrates a pilot symbol scrambling scheme according to a modality;

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Figure 4B - illustrates a pilot symbol scrambling scheme according to another modality;

Figure 5 - illustrates a base station with multiple sectors in a multiple access wireless communication system according to a modality;

Figure 6 - illustrates a multiple access wireless communication system according to another modality;

Figure 7 - illustrates a block diagram of a modality of a transmitting system and a receiving system in a multiple access and multiple output multiple access wireless communication system;

Figure 8 - illustrates a flow chart of a method of generating pilot symbols according to a modality;

Figure 9 - illustrates a flow chart of a method of changing pilot symbol patterns according to a modality; and

Figure 10 - illustrates a flow chart of a pilot pattern selection method.

Detailed Description of the Invention

With reference to Figure 1, a multiple access wireless communication system is illustrated according to a modality. A base station 100 includes multiple groups of antennas 102, 104 and 106 each including one or more antennas. In Figure 1, only one antenna is shown for each antenna group 102, 104 and 106, however, multiple antennas can be used for each antenna group that corresponds to a base station sector 100. Mobile station 108 is in communication with antenna 104, where antenna 104 transmits information to mobile station 108 via direct link 114 and receives information from mobile station 108 via reverse link 112. Mobile station 110 is in communication with antenna 106, where antenna 106 transmits information to mobile station 110 through the

6/38 direct link 118 and receives information from mobile station 110 through reverse link 116.

Each group of antennas 102, 104 and 106 and / or the area in which they are designed to communicate is often referred to as a base station sector. In the modality, antenna groups 102, 104 and 106 are individually designed to communicate with mobile stations in a sector, sectors 120, 122 and 124 respectively, in the areas covered by base station 100.

A base station can be a fixed station used to communicate with the terminals and can also be referred to as an access point, a Node B, or some other terminology. A mobile station can also be called a mobile station, user equipment (UE), a wireless communication device, terminal, access terminal or some other terminology.

Referring to Figure 2, a spectrum allocation scheme for a multiple access wireless communication system is illustrated. A plurality of OFDM 200 symbols are allocated through T symbol periods and S frequency subcarriers. Each OFDM 200 symbol comprises a symbol period of the T symbol periods and a tone or frequency subcarrier of the S subcarriers.

In an OFDM frequency hopping system, one or more symbols 200 can be assigned to a given mobile station. In an embodiment of an allocation scheme, as shown in Figure 2, one or more hop regions, for example, hop region 202 of symbols for a group of mobile stations for communication via a reverse link. Within each jump region, the assignment of symbols can be random to reduce potential interference and provide frequency diversity against harmful path effects.

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Each hop region 202 includes symbols 204 that are assigned to one or more mobile stations that are in communication with the base station sector and assigned to the hop region. In other modalities, each hop region is assigned to one or more mobile stations. During each jump period, or frame, the location of jump region 202 within the T symbol symbols and S subcarriers varies according to a jump sequence. In addition, the assignment of symbols 204 to the individual mobile stations within the hop region 202 may vary for each hop period.

The skip sequence can select pseudo-randomly, randomly, or according to a predetermined sequence, the location of skip region 202 for each skip period. The jump sequences for different sectors of the same base station are designed to be orthogonal to each other to avoid intracellular interference between mobile stations that communicate with the same base station. In addition, hop sequences for each base station can be pseudo-random with respect to hop sequences for nearby base stations. This can help to make intercellular interference between mobile stations in communication with different base stations random.

In the case of a reverse link communication, some of the symbols 204 of a hop region 202 are assigned to pilot symbols that are transmitted from the mobile stations to the base station. The assignment of pilot symbols to symbols 204 should preferably support multiple access by space (SDMA), where signals from different mobile stations overlapping the same hop region can be separated due to multiple receiving antennas in one sector or

8/38 base station, as long as there is sufficient difference in space signatures corresponding to different mobile stations. To extract more accurately and demodulate signals from different mobile stations, the respective reverse link channels must be estimated accurately. Therefore, it may be desired that pilot symbols on the reverse link allow the separation of pilot signatures from different mobile stations on each receiving antenna within the sector to subsequently apply multiple antenna processing to the pilot symbols received from different mobile stations.

Block jumping can be used for both the direct link and the reverse link, or just for the reverse link depending on the system. It should be noted that although Figure 2 represents the jump region 200 having a length of seven symbol periods, the length of the jump region 200 can be any desired quantity, it can vary in size between jump periods, or between different regions of jump. jump in a given jump period.

It should be noted that although the modality of Figure 2 is described in relation to the use of block jump, the block location does not need to be changed between consecutive jump periods or in any way.

With reference to Figures 3A and 3B, block diagrams of pilot assignment schemes are illustrated according to various modalities. Jump regions 300 and 320 are defined by T symbol periods by S subcarriers or tones. The jump region 300 includes pilot symbols 302 and the jump region 320 includes pilot symbols 322, with the remaining symbol periods and tone combinations available for data symbols and other symbols. In one mode, pilot symbol locations for each jump region, that is, a group of N_s contiguous tones over N_T

9/38 consecutive OFDM symbols, must have pilot tones located close to the edges of the jump region. This is usually because typical channels in wireless applications are relatively slow time and frequency functions so that a first-order approximation of the channel, for example, a first-order Taylor expansion, through the time and frequency hopping region provides information regarding channel conditions that are sufficient to estimate the channel for a given mobile station. As such, it is preferred to estimate a pair of channel parameters for adequate reception and demodulation of symbols from the mobile stations, namely, the constant component of the channel, a zero order term of a Taylor expansion, and the linear component , a first-order Taylor expansion of the channel through the span of channel frequency and time. Generally, the estimation accuracy of the constant component is independent of pilot placement. The estimation accuracy of the linear component is preferably obtained generally with pilot tones located at the edges of the jump region.

Pilot symbols 302 and 322 are arranged in groups of contiguous pilot symbols 304, 306, 308 and 310 (Figure 3A) and 324, 326, 328 and 330 (Figure 3b). In one embodiment, each cluster 304, 306, 308 and 310 (Figure 3A) and 324, 326, 328 and 330 (Figure 3b) within a jump region, have a fixed number, and often the same number, of pilot symbols within a given jumping region. The use of clusters 304, 306, 308 and 310 (Figure 3A) and 324, 326, 328 and 330 (Figure 3B) of contiguous pilot symbols can, in one modality, take into account the effect of multi-user interference caused by interference inter-carrier resulting from high Doppler and / or delayed symbol scattering.

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In addition, if pilot symbols from mobile stations programmed in the same hop region are received at substantially different power levels, signals from a stronger mobile station can create a significant amount of interference for a weaker mobile station. The amount of interference is higher at the edges, for example, subcarrier 1 and subcarrier S, of the hop region and also at the edge OFDM symbols, for example, symbol periods 1 and T, when the dispersion is caused by delay spread in excess, that is, when the portion of channel energy concentrated in the leads that exceed the cyclic prefix of the OFDM symbols becomes significant. Therefore, if pilot symbols are located only at the edges of a jump region, there may be degradation in channel estimation accuracy and a polarization in interference estimation. Consequently, as shown in Figures 3A and 3B pilot symbols are placed close to the edges of the jump region, however, avoiding the situation where all pilot symbols are at the edges of the jump region.

Referring to Figure 3A, a jump region 300 is comprised of pilot symbols. 302. In the case of channels with an increased frequency selectivity instead of time selectivity, pilot symbols 302 are located in groups of contiguous pilot symbols 304, 306, 308 and 310 with each pilot symbol group 304, 306, 308 and 310 covering multiple symbol periods a frequency tone. The frequency tone is preferably chosen to be close to the edges of the frequency range of the jump region 300, however, not quite at the edge. In the modality of Figure 3A, none of the pilot symbols 302 in a given cluster is in the tones of

11/38 edge frequency and in each cluster only pilot symbol can be in an edge symbol period.

The rationale behind a horizontal format of contiguous pilot symbol groupings of pilot symbols 302 is that, for channels with higher frequency selectivity, the first order (linear) component may be stronger in the frequency domain than in the domain of time.

It should be noted that one or more pilot symbols in each group, in the form of Figure 3A, may be in a different tone than one or more pilot symbols in a different group. For example, cluster 304 may be in pitch S and cluster 306 may be in pitch Sl.

With reference to Figure 3B, in the case of channels with an accentuated time selectivity instead of frequency selectivity, pilot symbols 322 are arranged in clusters 324, 326, 328 and 330 of contiguous pilot symbols that individually cover multiple frequency tones , but they have the same period of jump region symbols 320. OFDM symbols at the edges of the jump region 320, those that have a maximum tone, for example, S tone or minimum tone, for example, tone 1, of the frequency range that defines the S subcarriers, can be included as part of the pilot symbols , since there may be pilot symbols 322 that are at the edges of the jump region 320. However, in the modality shown in Figure 3B, only one pilot symbol in each group can be assigned to the maximum or minimum frequency subcarrier.

In the modality shown in Figure 3B, a channel with higher time selectivity may have a typical pattern that can be obtained by rotating 90 ° of the pattern chosen for channels with higher frequency selectivity (Figure 3A).

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It should be noted that one or more pilot symbols in each group, in the form of Figure 3B, can be assigned to a different symbol period than one or more pilot symbols in a different group. For example, cluster 324 may be in a different symbol T period than cluster 326.

In addition, as shown in the modalities of Figures 3A and 3B, pilot patterns are provided so that groupings 304, 306, 308 and 310 (Figure 3A) and 324, 326, 328 and 330 (Figure 3B), are preferably symmetrical with relation to the center of the jumping region. The symmetry of the clusters with respect to the center of the region

<td>jumping</td><td>can</td><td colspan="4">provide simultaneous estimation</td><td>perfected</td><td>of</td>

<td colspan="3">channel with relation</td><td>The</td><td>answers</td><td>of time</td><td>and frequency</td><td>of</td>

<td>channel.</td><td>It should</td><td>to be</td><td colspan="2">observed that</td><td>although the</td><td>Figures 3A and</td><td>3B</td>

represent four groupings of pilot symbols per jump region, a smaller or greater number of groupings can be used in each jump region. In addition, the number of pilot symbols per pilot symbol cluster can also vary. 0 total number of pilot symbols and groupings of pilot symbols is a function of the number of pilot symbols required by the base station to successfully demodulate data symbols received on the reverse link and estimate the channel between the base station and the mobile station. In addition, each grouping does not need to have the same number of pilot symbols. The number of mobile stations that can be multiplexed over a single hop region can, in one mode, be equal to the number of pilot symbols in a hop region.

In addition, although Figures 3A and 3B represent groupings of designated pilot symbols or for channels having frequency selectivity or time selectivity o

13/38 pilot pattern can be such that there are groupings for frequency selective channels as well as groupings for time selective channels in the same pilot pattern, for example, some groupings arranged in the 304, 306, 308 or 310 group pattern and some clusters arranged in the cluster pattern 324, 32 6, 328 or 330.

In some modalities, the pilot pattern chosen to be used can be based on the conditions for which the channel is being optimized. For example, for channels that can move at high speed, for example, from mobile stations, a time selective pilot pattern may be preferred, whereas

<td>movement</td><td colspan="2">speed</td><td>slow</td><td>in</td><td>station</td><td>mobile, for</td>

<td>example,</td><td>pedestrians,</td><td>one</td><td>standard</td><td>in</td><td>pilot</td><td>selective on</td>

<td>frequency</td><td>Can be</td><td colspan="2">used.</td><td>In</td><td colspan="2">another modality, the</td>

<td>pattern of</td><td>pilot can</td><td>to be</td><td colspan="2">chosen</td><td>based</td><td>under conditions</td>

channel, a determination made after a predetermined number of jump periods.

With reference to Figures 3C-3E, additional pilot patterns are shown. In Figure 3C, a block is represented as having a pilot pattern similar to that of 3B, except that there are a greater number of clusters, for example, 9, and the block size has changed. Additional pilots can be used to improve channel estimation properties. It should be noted that the number of groups and pilots per group may vary depending on a user's measured speed, for example, a higher speed user may have more groupings, and / or pilots per group, than a user with a speed smaller.

In Figure 3D, a pilot pattern with additional pilots for frequency selective conditions is included. This can be useful for users with channels

14/38 highly selective in frequency, which can in some aspects, be detected based on users' delay spreading estimates. In addition, channel statistics in relation to time for user or cell or sector session information to calculate a specific user, sector or cell limit to switch to these standards with additional pilots. Additional pilots can be quite useful due to frequency and multipath variations that will vary due to different channel conditions at different frequencies, for example, for mobile users or others having greater frequency selectivity.

In Figure 3E, pilot groupings for mobile stations with multiple inputs and multiple outputs (MIMO) that are transmitting multiple layers are represented. Each transmission antenna, here being four, includes pilot symbols in the cluster. Therefore, if fewer than all the antennas are being used then fewer pilots can be included in each cluster.

With reference to Figures 4A and 4B, pilot allocation schemes according to additional modalities are illustrated. In Figure 4Ά, jump regions 400 include pilot symbols Ci,_q, C2,_q, and C₃,_q, arranged in cluster 402; Ç₄,_q, Ç₅,_q, and C6,_q, arranged in cluster 404; C7,_q,

Cs, q, and C₉,_q, arranged in cluster 408; and Cio,_q, Cn,_q, and Ci2, q, arranged in cluster 406. In one mode, to improve spatial diversity in jump regions where multiple mobile stations provide pilot symbols in overlap, the pilot symbols of different mobile stations must be multiplexed in such a way that over the same period of OFDM and tone symbols so that the

15/38 pilot symbols are substantially orthogonal when received at the base station cluster's antennas.

In Figure 4A, each of the pilot symbols Ci,_{q /}0-2, q, 0-3, q, C_4zq_z Cs_zq_z C-6_zq_z Cg, q, ^ 9_zq_z C10, q, Cll_zq_z ® Ci2, q θ assigned to multiple mobile stations in the hop region 400, that is, each symbol period includes multiple pilot symbols, from a number of different mobile stations. Each of the pilot symbols in a pilot symbol cluster, for example, cluster 402, 404, 406 and 408, is generated and transmitted in such a way that a receiver of the pilot symbols in the cluster, for example, base station, can receive the same so that they are orthogonal to the pilot symbols from each other mobile station in the same cluster. This can be done by applying a predetermined phase shift, for example, a scalar function to multiply, each of the samples constituting the pilot symbols transmitted by each of the mobile stations. To provide orthogonality, the internal products of vectors representing the sequence of scalar functions in each cluster for each mobile station can be zero.

Additionally, in some embodiments, it is preferred that the pilot symbols of each group are orthogonal to the pilot symbols of each other group in the jump region. This can be provided in the same way that orthogonality is provided for pilot symbols within each cluster from a different mobile station, by using a different sequence of scalar functions for the pilot symbols of each mobile station in each cluster of symbols pilot. The mathematical determination of orthogonality can be done by selecting a sequence of multiple scalars for each of the pilot symbols for a specific grouping

16/38 for the mobile station specifies whose vector is orthogonal, for example, whose internal product is zero, with respect to a vector representing the sequence of multiple scalars used for the pilot symbols of the other mobile stations in all clusters and the same station mobile in the other groupings.

In one mode, the number of mobile stations that can be supported, where orthogonality of the pilot symbols across each group is provided, is equal to

<td>number of</td><td>symbols</td><td>pilot who</td><td colspan="2">are</td><td colspan="2">provided by</td>

<td>grouping</td><td>of symbol</td><td>pilot.</td><td></td><td></td><td></td><td></td>

<td>At</td><td colspan="2">modality of the Figures</td><td>4A</td><td>and</td><td>4B,</td><td>the q-th</td>

<td>user of</td><td>Q users</td><td>overlapping,</td><td> 1 &lt;</td><td> 9</td><td></td><td>uses the</td>

<td>string S</td><td>of size</td><td>Np, where N_P it's the</td><td colspan="4">total number of tones</td>

pilots (in Figures 4A and 4B, Np-12) '.

d) here () indicates transposition of the matrix containing the sequences. As discussed above, the sequences of scalar functions, in each group of pilot symbols, must be different for different mobile stations to obtain compatible estimates of the respective channels by reducing interference between pilot symbols. In addition, sequences must be linearly independent, since it is preferred that no sequence or vector is a linear combination of the remaining sequences. Mathematically, this can be defined in which the NpxQ (2) matrix

17/38 is a total column order. It must be observed in expression (2) above matrix Q &lt;Np. That is, the number of overlapping mobile stations must not exceed the total number of pilot symbols in the jump region.

Based on the above, any set of Q strings with a total order S enables compatible channel estimation. However, in another modality, the effective estimation precision may depend on the correlation properties of S. In one modality, as can be determined using equation (1), performance can be improved when any two sequences are mutually (almost) orthogonal. in the presence of the channel. Mathematically, this condition can be defined by

Σ H_ks_ktPs_k* «0 for all \ &lt;p, q &lt;Q, * = 1 (3) where H / ç is a complex channel gain corresponding to the kth pilot symbol, 1 &lt;k &lt;Np. In a time and frequency invariant channel condition Hi = H2 = ... = Hm&gt; (3) reduces to the requirement for mutually orthogonal sequences:

P^aratodo (4) i = l imposing this condition on any possible channel realization from a typical set of channels may be impractical. In reality, expression (3) can be satisfied when a channel has limited selectivity in time and frequency, which is the case of pedestrian channels with a relatively small delay spread. However, conditions can be substantially different in vehicle channels and / or

18/38 channels with significant delay spread, thereby resulting in performance degradation.

As discussed with respect to Figures 3A and 3B, pilot allocation patterns consist of some groupings of pilot symbols placed close to the edges of the jump region, where each group is contiguous in time (Figure 3A) and / or frequency (Figure 3B) . Since channel variations within each cluster are generally limited, due to the contiguous nature of the pilot symbols in time and frequency and the continuity of the channel in time and frequency. Consequently, making different sequences orthogonal on each cluster allows condition (3) to be met. A potential disadvantage of this solution is that the number of overlapping mobile stations that can be orthogonal on each cluster is limited to the cluster size, indicated here by N_ç. In the example shown in Figures 4A and 4B, Nc = 3, and therefore even Q = 3 mobile stations can be separated orthogonally in one mode. In reality, a relatively small number of Q is sufficient in many practical scenarios. When Q&gt; N_ç, it can be difficult to keep all mobile stations orthogonal on each cluster, since there may be some inter-symbolic interference. Consequently, approximate orthogonality may be sufficient, with a little loss of performance of time and / or frequency variation channels if Q&gt; N_Ç.

In one embodiment, a set of design parameters for the scalar function sequences S = [S] ... Sq / can be defined by:

* any two strings are orthogonal over the entire set of pilot symbols, thereby meeting

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T^sm^sm⁼⁰ for all l &lt;p, q &lt;Q,

4 = 1 (5) * Subsequent groups of Nc sequences are such that any two sequences in a group are mutually orthogonal to any group of pilots:

= Q, nN_ç +1 &lt;p, q &lt;min {(»+ l) #_ç, Q}, 0 &lt;n &lt;0 &lt;l &lt;M_ç. (6) * = i Al_ç * all elements of all sequences have substantially equal absolute values, for example approximately the same power.

where Mc denotes the total number of size clusters

N_ct so that the number of pilots Np = McNcIn a modality, the sequences S = [Sj ... SqJ are created using exponential functions of energy mode by symbol by symbol provided that the same for each sequence.

In addition, in this modality, groups of sequences

Nc can be mutually orthogonal within each grouping, regardless of grouping size since exponents are not limited to specific multiples, and with the strings used in each other grouping across all pilot symbols, by (i) defining exponential sequences within each grouping; and (ii) populate the intra-group parts through groupings. This can be seen in equation (7) where a base of Discrete Fourier Transform NxN (DFT) is defined.

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F (7V) = 'F ^ N)

FjN)

Z2jr— e ^N

12π— and ^N / 2 ^ e ^N (7) expression above

12.01 and

π, ΟμΧΜ and

written in a compact block form as follows:

s = [s „..., s_q] = {f (m_ç) s&gt; f (n_ç)}_{j: Q} (8) where θ indicates matrix block covering columns 1 through Q of the original matrix. A more general form of S can be given by:

s = [s, ..... S_Q] ^ {V®U}_{: tQ} (9) where U is an arbitrary NqxNc unit matrix (U * U = I ^ p) and V is an arbitrary MqxMq unit matrix (U * U = Imc) ·

In one embodiment, the number of mobile stations that can be supported, where orthogonality of the pilot symbols across each group is provided, is equal to the number of pilot symbols that are provided per pilot symbol cluster.

In one embodiment, the exponential functions used to multiply the samples of the pilot symbols are generated using a discrete Fourier transform function, which is well known. In modalities where the discrete Fourier transform function is used to generate the symbols for transmission, an extra phase shift is applied during symbol formation using the discrete Fourier transform function in the generation of the symbols for transmission.

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In the modalities of Figures 4A and 4B, the internal products of vectors that represent the sequence of scalar functions in each cluster for each mobile station can be zero. However, in other modalities this is not the case. It can be arranged so that only semi-orthogonality between the sequences of the scalar functions in each cluster for each mobile station is provided.

In addition to these situations where the number of mobile stations assigned to the hop region is less than the number of pilot symbols assigned to the hop region, the scalar displacements can still be decoded at the base station to be used to perform interference estimation. Therefore, these pilot symbols can be used for interference estimation since they are orthogonal or semi-orthogonal with respect to pilot symbols by the other mobile stations assigned to the jump region.

The approaches described with respect to Figures 4A and 4B can be applied to the grouping and structures represented in Figures 3C-3E. In such cases, the length and number of strings may need to vary to support the number of groupings and the number of pilot symbols per group.

Referring to Figure 5, a multi-sector base station in a multiple access wireless communication system according to a modality is illustrated. A base station 500 includes multiple antenna groups of antennas 502, 504 and 506. In Figure 5, only one antenna is shown for each antenna group 502, 504 and 506, however multiple antennas can be used. The multiple antennas of each antenna group 502, 504 and 506 can be used to provide spatial diversity at the base station for signals transmitted from mobile stations in a corresponding sector, in addition to diversity

22/38 space provided for the different physical locations of the different mobile stations.

Each group of antennas 502, 504 and 506 of base station 500 is configured to communicate with mobile stations in a sector to be covered by base station 500. In the form of Figure 5, the group of antennas 502 covers sector 514, group antenna 504 covers sector 516, and antenna group 506 covers sector 518. Within each sector, as described in relation to Figure 4, pilot symbols transmitted from mobile stations can be accurately demodulated and used for channel estimation, and other functionality, at the base station due to the approximate orthogonality or orthogonality between all intersector pilot symbol groupings.

However, intra-sectoral interference may exist for mobile stations close to the limit of a sector, for example, mobile station 510 which is close to a limit of sectors 514 and 516. In such a case, pilot symbols from mobile station 510 may be at lower powers than the pilot symbols from other mobile stations in both sectors 514 and 516. In such a situation, mobile station 510 could eventually benefit from reception on both sector antennas, especially when its channel for the sector in service, that is, sector signals 516 may fade if the power is increased from antenna 504 To fully benefit from reception from antenna 502 in sector 514, an accurate estimate of the channel of mobile station 510 between antennas 502 in sector 514 must be provided. However, if the same or substantially the same sequences are used for the scalar multiple of the pilot symbols in different sectors with the present pilot project, pilot symbols transmitted by mobile station 510 may collide with pilot symbols

23/38 transmitted by mobile station 508 which is programmed in sector 514 in the same hop region as mobile station 510 is programmed in sector 516. In addition, in some cases depending on the power control strategy used by the base station to control mobile stations, the symbol power level from mobile station 508 can substantially exceed the signal level of mobile station 510 in the antenna group. 502 of sector 514, especially when mobile station 508 is close to base station 500.

To combat the intra-sectoral interference that can originate, scrambling codes can be used for mobile stations. The scrambling code can be unique for individual mobile stations or they can be the same for each of the mobile stations that communicate with an individual sector. In one embodiment, these specific scrambling codes allow the antenna group 502 to view a channel composed of mobile stations 508 and 510.

In the case where a single mobile station is assigned to an entire hop region, user-specific scrambling sequences can be provided so that every mobile station in a given sector makes use of the same pilot sequence; the construction of these sequences is described in relation to Figures 4A and 4B. In the example in Figure 5, mobile stations 508, 510 and 512 can have different user-specific scrambling sequences and therefore sufficient channel estimation can be achieved.

Where multiple mobile stations are or can be assigned to the same hop region, two approaches can be used to reduce intra-cluster interference. First, user-specific scrambling strings can be used

24/38 if the Nc cluster size is greater than or equal to the number of overlapping mobile stations in each sector Q times the number of sectors in the cell. If this is the case, different sets of different user-specific Q scrambling codes can be assigned to different sectors.

However, if the Nc cluster size is less than the number of overlapping mobile stations in each sector Q times the number of sectors in the cell, this may be important if a system design objective is to maintain N_ç to maintain limited pilot overhead, user-specific scrambling codes may not be effective in reducing intercellular interference. In such cases, a sector-specific scramble sequence can be used in conjunction with the user-specific scramble sequence.

A sector-specific scrambling sequence is a sequence Xs = [Xi, 2, -, Xnp.s] of Np complex functions that multiply the respective elements of the sequences S = [S] ... Sq], for all stations furniture in the same sector. In a cell consisting of S sectors, a set of S sector-specific scrambling sequences Xi, ..., Xs can be used to multiply the S = [Si ... Sq] sequences of the mobile stations. In such a case, mobile stations within different sectors, for example, sector 514.e 516 which may have mobile stations that use the same user-specific scrambling sequences S = [Si ... Sq] may differ due to different sequences of sector-specific scrambling Jf_5i and X_Si used to multiply the user-specific scramble sequence.

Similar to user-specific scrambling, it is preferred that all entries for Χι,.,., Χς have

25/38 absolute values ​​approximately equal to maintain approximately equal power between the pilot symbols. In other modalities, it is preferred that entries of Xi, ..., X_sare such that any pair of pilot symbols in a group of pilot symbols, corresponding to any two combinations of user-specific and sector-specific scrambling sequences, must satisfy condition (3). One way to address the choice of content for each specific sector sequence Xi, ..., Xs consists of an exhaustive search for sequences as the elements of the entire sequence are taken from the same constant module constellation (PSK) as QPSK, 8- PSK. The selection criterion can be based on the worst case channel estimation error variance corresponding to the worst combination of mobile stations from different sectors and specific shuffles from different users that are based on the potential channel environment. The channel estimation error can be computed analytically based on the channel's statistical properties. Specifically, a trace of the covariance matrix of a channel estimate that assumes a channel correlation structure based on an early fading model and parameters such as mobile station speed, which defines selectivity over time, and propagation delay spread that defines selectivity. in frequency. Analytical expressions for the minimum obtainable channel estimation error subject to one of the true channel correlation structure are known in the art. Other similar criteria can be used to also optimize the choice of Χι, ..., Χ $ ·

In a modality where Quadrature Amplitude Modulation is used as the modulation scheme, a set of specific

26/38 sector Xi, ..., Xs that can be used is shown in the Table below. Each entry in the table specifies components I and Q of each X ^, l &lt;s &lt;S and 1 &lt;k &lt;Np with S = 3 and Np = 12.

Table 1

<td>k</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td><td> 9</td><td> 10</td><td> 11</td><td> 12</td>

<td>S =</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td> (+1,+</td><td>(+ i, +</td>

<td> 1</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td><td> 0}</td>

<td>s =</td><td> {+1, +</td><td> {+1, +</td><td> {-</td><td>(+ i, +</td><td> {+0,-</td><td> (+1, +</td><td> {+1,+</td><td> {+0,-</td><td>í + 0, +</td><td> (+0,+</td><td> (+0,+</td><td> {+0, +</td>

<td> 2</td><td> 0}</td><td> 0}</td><td> 1,+0}</td><td> 0}</td><td> 1}</td><td> 0}</td><td> 0}</td><td> 1}</td><td> 1}</td><td> 1}</td><td> 1}</td><td> 1}</td>

<td>S =</td><td> {+0,+</td><td> {-1,</td><td> (+1,+</td><td> (+1,+</td><td> (+0,+</td><td> {+0,-</td><td> {+0,-</td><td> {+0,-</td><td> (+1, +</td><td> {+0,-</td><td> (+1,+</td><td> {-1,</td>

<td> 3</td><td> 1}</td><td> +0}</td><td> +0}</td><td> 0}</td><td> 1}</td><td> 1}</td><td> 1}</td><td> 1}</td><td> 0}</td><td> 1}</td><td> 0}</td><td> +0}</td>

In some embodiments, each cell in a communication network can use the same sequences for sector-specific scrambling sequences.

With reference to Figure 6, a multiple access wireless communication system 600, according to another mode, is illustrated. In the case where the same sets of user-specific and sector-specific scrambling sequences are used in multiple cells, for example, cells 602, 604 and 606, interference from adjacent cells can lead to degradation of channel estimation accuracy due to the collision of pilot symbols. For example, a channel estimate within the sector of interest can be polarized by the channel of a mobile station from the adjacent cell whose mobile station has the same user-specific and sector-specific scrambling. To avoid such polarization, a specific cell scramble can be used,

<td colspan="2">beyond shuffling</td><td>specific</td><td>in</td><td>user</td><td>and</td>

<td>shuffle</td><td>specific</td><td>sector.</td><td>a</td><td>scheme</td><td>in</td>

<td>shuffle</td><td>specific to</td><td>cell can</td><td>to be</td><td>defined</td><td>per</td>

T

Y_ç = [Yi,_The-&gt; Ynp, J which is a vector of scalar functions that multiply the respective sequence of pilot symbols to

27/38 each mobile station in the cell. The general sequences of pilot Z symbols (_qAC) = [Zi_i(q_iStc), ..., ZNP (_qAc)] that correspond to a mobile station with a user-specific q-th scramble in the s-th sector of the c-th cell can be defined as follows. If sector-specific scrambling is used:

\ &lt;k &lt;N_P, (10)

If sector-specific scrambling is not used:

Z_kM= S_ktg-Y_ktC, l &lt;k &lt;N_P, l &lt;s &lt;S, c = l, 2, .... (11)

As already mentioned, the use of sector-specific scrambling is recommended when Q&gt; 1 and is not recommended when Q = 1.

Unlike user-specific and sector-specific scrambling, no specific optimization of cell-specific scrambling sequences needs to be used. The two design parameters that can be used are that:

* all elements of cell-specific scrambling sequences have equal modulus.

* cell-specific scrambling sequences differ substantially for different cells.

In the absence of predetermined assignment of cell-specific scrambling sequences over a network of base stations, a cell-specific (pseudo) random scrambling sequence from some constant module constellation (PSK) such as QPSK, 8-PSK can be used in the formation of specific Y cell sequences. To further increase the randomization of specific cell scrambling and avoid combinations

28/38 bad shuffle sequence constants, cell-specific shuffling can be changed periodically in a (pseudo) -random mode. In some modalities, the periodic change can be the whole frame, super frame or multiple frames or super frames.

Figure 7 is a block diagram of a modality of a transmitting system 710 and a receiving system 750 in a MIMO 700 system. In the transmitting system

710, traffic data for various data streams is provided from a data source 712 to a transmission data processor (TX) 714. In one embodiment, each data stream is transmitted via a respective transmission antenna. The TX 714 data processor formats, encodes, and merges traffic data for each data stream based on a specific coding scheme selected for that data stream to provide encrypted data.

The encoded data for each data stream can be multiplexed with pilot data using OFDM techniques. Pilot data is typically a known data pattern that is processed in a known manner and can be used in the receiving system to estimate the channel response. The multiplexed encoded and pilot data for each data stream is then modulated (that is, mapped into symbols) based on a specific modulation scheme (for example, BPSK, QSPK, M-PSK or MQAM) selected for that data stream to provide modulation symbols. The data rate, encoding and modulation for each data stream can be determined by executed instructions provided by the controller 130.

The modulation symbols for all data streams are then provided to a TX 720 processor, which can further process the modulation symbols (eg

29/38 example, for OFDM). The TX 720 processor then provides Nt modulation symbol streams for Nt transmitters (TMTR) 722a through 722t. Each transmitter 722 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters and upwards converts) the analog signals to provide a modulated signal suitable for transmission through the MIMO channel. N_T signals modulated from transmitters 722a through 722t are then transmitted from Nt antennas 124a through 124t, respectively.

In the receiving system 750, the transmitted modulated signals are received by N_R antennas 7 52a through 7 52r and the signal received from each antenna 752 is supplied to a respective receiver (RCVR) 754. Each receiver 754 conditions (for example, filters, amplifies and downwards converts) a respective received signal, digitizes the signal conditioned to provide samples, and further processes the samples to provide a corresponding received symbol stream.

An RX 760 data processor then receives and processes the Nr symbol streams received from Nr receivers 754 based on a specific receiver processing technique to provide Nt detected symbol streams. Processing by the RX 760 data processor is described in further detail below. Each stream of symbols detected includes symbols that are estimates of the modulation symbols transmitted to the corresponding data stream. 0 RX 760 data processor then demodulates, deinterleaves, and decodes each detected symbol stream to retrieve traffic data for the data stream. Processing by the RX 760 data processor

30/38 is complementary to that performed by the TX 720 processor and TX 714 data processor in the transmitting system 710.

The TX 760 processor can derive an estimate of the channel response between the transmitting antennas Nr and receiving antennas Nr, for example, based on the pilot information multiplexed with the traffic data. The RX 760 processor can identify pilot symbols according to pilot patterns stored in memory, for example, memory 772, which identify the frequency sub-carrier and symbol period assigned to each pilot symbol. In addition, user, sector, and cell-specific scrambling sequences can be stored in memory so that they can be used by the RX 760 processor to multiply the received symbols so that proper decoding can take place.

The channel response estimate generated by the RX 760 processor can be used to perform space, space / time processing on the receiver, adjust power levels, change modulation rates or schemes, or other actions. The RX 760 processor can further estimate the signal-to-noise and interference ratios (SNRs) of the detected symbol streams, and possibly other channel characteristics, and provides these quantities for a 770 controller. 0 RX 760 data processor or 770 controller can additionally derive an estimate from the operating SNR for the system. The controller 770 then provides channel status information (CSI), which can comprise various types of information regarding the communication link and / or data stream received. For example, CSI can understand only the SNR in operation. The CSI is then processed by a TX 778 data processor, which also receives traffic data for a number of

31/38 data from a data source 77 6, modulated by a modulator 780, conditioned by transmitters 754a through 754h, and transmitted back to the transmitting system 710.

In the transmitting system 710, the signals modulated from the receiving system 750 are received by the antennas 724, conditioned by the receivers 722, demodulated by a demodulator 740, and processed by an RX data processor 742 to recover the CSI reported by the receiving system. The reported CSI is then provided to the 730 controller and used to (1) determine the data rates and modulation and encoding schemes to be used for the data streams and (2) generate various controls for the TX 714 data processor and TX 720 processor.

Controllers 730 and 770 guide operation in the transmitter and receiver systems, respectively. Memories 732 and 772 provide storage for program codes and data used by controllers 730 and 770, respectively. Memories 732 and 772 store pilot patterns in terms of cluster locations, user-specific scrambling sequences, sector-specific scrambling sequences, if used, and cell-specific scrambling sequences, if used. In some embodiments, multiple pilot patterns are stored in each memory so that the transmitter can transmit and the receiver can receive both frequency-selective pilot patterns and time-selective pilot patterns. In addition, pilot patterns in combination having groupings equipped for time selective channels and frequency selective channels can be used. This allows a transmitter to transmit a specific standard based on a parameter,

32/38 as a random sequence, or in response to an instruction from the base station.

Processors 730 and 770 can then select which of the pilot patterns, user-specific scrambling sequences, sector-specific scrambling sequences, and cell-specific scrambling sequences should be used in the transmission of pilot symbols.

At the receiver, various processing techniques can be used to process the received Nr signals to detect the transmitted Nr symbol streams. These receiver processing techniques can be grouped into two main categories (i) time-space and spatial receiver processing techniques (which are also referred to as equalization techniques); and (ii) interference cancellation receiver processing technique and successive equalization / cancellation (which is also referred to as successive interference cancellation or successive cancellation processing technique).

Although Figure 7 illustrates a MIMO system, the same system can be applied to a single input multiple input system where multiple transmit antennas, for example, those at a base station, transmit one or more streams of symbols to an antenna device for example, a mobile station. In addition, a single exit antenna system for single entry can

<td colspan="5">be used in the same way as described</td><td>with</td><td>relationship</td><td>The</td>

<td>Figure 7.</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>With</td><td colspan="2">reference to</td><td>Figure</td><td>8, is</td><td colspan="2">illustrated</td><td>one</td>

<td>flowchart</td><td>one</td><td>method of</td><td>generation</td><td colspan="2">of symbols</td><td>pilot</td><td>in</td>

according to a modality. A plurality of pilot symbol groupings are selected to be transmitted

33/38 during a hop region from a specific mobile station, block 800. These groupings of pilot symbols can all be aligned for transmission on a frequency-selective (Figure 3A), time-selective (Figure 3B) or one combination of clusters some of which are aligned for transmission on a frequency-selective and time-selective channel. In addition, pilot groupings can be selected based on whether there is a high degree of mobility for the user. This can be done to improve channel estimation at the base station. In addition, the number of antennas used for transmission at the mobile station, as well as the number of information flows being transmitted from those antennas, the number of selected clusters and the number of pilot symbols per cluster can be used.

After selecting the pilot symbol groupings, a determination is made as to whether the base station group on which the mobile station is communicating supports, or is in communication with, multiple mobile stations, block 802. This determination can be based on predetermined knowledge of the network on which the mobile station. Alternatively, this information can be transmitted from the sector to the base station as part of its broadcast messages or pilot information.

If the cluster does not support communication, or is not currently in communication with multiple mobile stations, then scalar functions are applied to the pilot symbols that are unique to the cluster with which the mobile station is in communication, block 804. In one mode, the scalar functions for each sector can be stored in the mobile station and used depending on a sector identification signal that is part of its part of its broadcast messages or pilot information.

34/38

If the cluster effectively supports communication with multiple mobile stations, then scalar functions are applied to the pilot symbols that are unique to the mobile station, block 806. In some modalities, the scalar functions for each mobile station can be based on its unique identifier used for registration or supplied to the device at the time of manufacture.

After the scalar functions, which are unique or for the sector with which the mobile station is communicating or the mobile station itself, are applied to the pilot symbols, another sequence of scalar functions is applied to the pilot symbols, block 808. The sequence of scalar functions refers to the cell in which the mobile station is communicating. This scalar function can vary over time, if each cell is not specifically assigned scalar functions that are known to or provided to mobile stations. After this operation, the pilot symbols can be transmitted from the mobile station to the base station.

The scalar functions discussed with respect to Figure 8, may in one embodiment involve a phase shift of each of the samples that constitute the pilot symbols. As discussed with respect to Figures 4A, 4B, 5 and 6, scalar functions are selected so that each group of pilot symbols is orthogonal to each other set of pilot symbols from the same base station in other groupings of pilot symbols and in same and other groupings of pilot symbols for other mobile stations in the same sector as the base station.

In addition, the blocks described in relation to Figure 8 can be implemented as one or more instructions in a computer-readable medium, such as a

35/38 memory, which are implemented by a processor, controller, or other electronic circuitry.

Referring to Figure 9, a flow chart of a method of changing pilot symbol patterns according to an embodiment is illustrated. Information regarding channel conditions is obtained, block 900. The information can comprise SNR relationships at one or more mobile stations, a channel selectivity, the type of traffic, pedestrian or vehicular, delay spread, or other characteristics of the channel. This information can be determined by the base station or it can be provided as channel quality feedback information provided from the mobile station.

The information is analyzed to determine channel conditions, block 902. The analysis can be a determination of whether the channel is selective in frequency, in time, or a combination of both. The analysis is then used to determine a pilot symbol pattern that must be transmitted from the mobile stations that can communicate with the sector or base station, block 904. These pilot symbol groupings can all be aligned for transmission on a frequency selective channel (Figure 3A), time selective (Figure 3B), a combination of groupings some of which are aligned for transmission on a frequency selective channel and a channel time selective, used for vehicular traffic or other mobile traffic (Figure 3D), optimized for a MIMO system (Figure 3E) or combinations thereof. The specific pilot pattern selected can then be used by all mobile stations that communicate with the base station or sector until such time that the diagnosis is performed again for the base station or sector.

36/38

To implement a specific pilot pattern on mobile stations that communicate at a base station or base station sector, an instruction can be sent from the base station or sector to the mobile stations as part of the initialization or setup procedure. In some modalities, information such as which pilot pattern, user-specific scrambling sequence, sector-specific scrambling sequence, and / or cell-specific scrambling sequence should be used, can be transmitted in a preamble of one or more packets of data that is transmitted from a base station to a mobile station at regular intervals or during initialization or configuration.

It should be noted that the analysis can also be used to determine the number of pilot symbols to be transmitted in each group of pilot symbols and groupings of pilot symbols. In addition, the blocks described with reference to Figure 9 can be individually implemented as one or more instructions in a computer-readable medium, such as a memory or removable medium, which are implemented by a processor, controller or other electronic circuitry.

Referring to Figure 10, a flow chart of a pilot pattern selection method is illustrated. A determination is made with respect to the frequency selectivity of a given user, block 1000. This can be done, for example, based on a user speed, a user Doppler spread, user delay spread, or other information from channel that can be used, user conditions related to mobility. This information can then be used to select one or more from a plurality of pilot patterns for transmission by the user to the base station,

37/38 block 1002. The selection may include, for example, a number of pilots to transmit and the number of pilots in total and by group. In addition, the selection may include information regarding whether the user is a MIMO 5 user as well as user mobility. The selection can be made by determining the frequency selectivity ratio of the user and some frequency selective limit determined by channel statistics for the user, sector, or cell over one or more periods of time. An indication of the pilot pattern is then transmitted to the user, so that the user can use the pilot pattern in later transmissions to the base station, block 1004.

It should be noted that although Figure 10 illustrates that the base station can make the determination regarding user mobility, the same approach can be used by the mobile station. In this case, block 1000 can be executed based on direct link pilots transmitted by the base station, and block 1004 can be omitted.

The techniques described here can be implemented by various means. For example, these techniques can be implemented in hardware, software, or a combination of them. For a hardware implementation, the processing units in a base station or a mobile station can be implemented in one or more 25 application-specific integrated circuits (ASICs),

<td>processors</td><td>in</td><td>signals</td><td>digital</td><td>(DSPs),</td><td>devices</td><td>in</td>

<td>processing</td><td>in</td><td>signals</td><td>digital</td><td>(DSPDs),</td><td>devices</td><td>in</td>

<td colspan="3">programmable logic (PLDs)</td><td>matrix</td><td>of doors</td><td>programmable</td><td>in</td>

field (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described here, or a combination of them.

38/38

For a software implementation, the techniques described here can be implemented with modules (for example, procedures, functions, and so on) that perform the functions described here. Software codes can be stored in memory units and executed by processors. The memory unit can be implemented in the processor or external to the processor, in which case it can be communicatively coupled to the processor through various means as known in the art.

The foregoing description of the described modalities is provided to allow anyone skilled in the art to make or use the present invention. Various modifications to these modalities can be readily apparent to those skilled in the art, and the generic principles defined here can be applied to other modalities without departing from the inventive concept or scope of the invention. Thus, the present invention is not intended to be limited to the modalities shown here, but the broader scope compatible with the principles and new aspects described here must be agreed.