Closed Loop Resource Allocation in a High Speed Wireless Communications Network

ES 2 398 872 T3

DESCRIPTION

Closed-loop resource allocation in a high-speed wireless communications network

Background of the invention

I. Field of the invention

The present invention relates to wireless communications. More particularly, the present invention relates to a new and improved method and apparatus for determining transmission data rates in a high speed wireless communication system.

II. Description of Related Art

Today a communication system is required to support a variety of applications. One such communication system is a code division multiple access (CDMA) system which is in accordance with “TIA / EIA / IS-95 Base Station-Subscriber Station Compatibility Standard for Broadband Spread Spectrum Cellular System Dual Mode ”, hereinafter referred to as the IS-95 standard. The CDMA system allows voice and data communications between users over a terrestrial link. The use of CDMa techniques in a multiple access communication system is disclosed in US Patent No. 4,901307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", and in US Patent No. 5,103 .459, entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", both assigned to the assignee of the present invention.

In the present specification, base station refers to the hardware with which the subscriber stations communicate. Cell refers to hardware or geographic coverage area, depending on the context in which the term is used. A sector is a partition of a cell. Because a sector of a CDMA system has the attributes of a cell, the teachings described in terms of cells are easily extended to sectors.

In the CDMA system, communications between users are conducted through one or more base stations. A first user at a subscriber station communicates with a second user at a second subscriber station by transmitting data on the reverse link to a base station. The base station receives the data and can route the data to another base station. The data is transmitted on the forward link from the same base station, or a second base station, to the second subscriber station. Forward link refers to transmission from the base station to a subscriber station and reverse link refers to transmission from the subscriber station to a base station. In IS-95 systems, separate frequencies are assigned to the forward link and the reverse link.

The subscriber station communicates with at least one base station during a communication, CDMA subscriber stations are capable of communicating with multiple base stations simultaneously during the call transfer. Call transfer is the procedure of establishing a link with a new base station before severing the link with the old base station. Call transfer minimizes the likelihood of dropped calls. The method and system for providing communication with a subscriber station through more than one base station during the call transfer procedure is disclosed in US Patent No. 5,267,261, entitled "MOBILE ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM ”, assigned to the assignee of the present invention. Call transfer is the procedure in which communication occurs over multiple sectors that are served by the same base station. The procedure for transferring calls is described in detail in the United States Patent Application pending together with the present one with Serial No. 08 / 763,498, entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION", filed on December 11, 1996, assigned to the assignee of the present invention.

Given the increasing demand for wireless data applications, the need for highly efficient wireless data communication systems has become increasingly significant. The IS-95 standard is capable of transmitting traffic data and voice data over the forward and reverse links. A procedure for transmitting traffic data in fixed-size code channel frames is described in detail in United States Patent No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION", assigned to the assignee of the present invention. According to the IS-95 standard, traffic data or voice data is subdivided into code channel frames that are 20 ms wide with data rates as high as 14.4 Kbps.

A fully specialized system for high-speed wireless communications is disclosed in co-pending United States Patent Application Serial No. 08 / 963,386 (the '386 application), filed November 3, 1997, entitled , "METHOD AND APPARATUS FOR HIGHER RATE PACKET DATA TRANSMISSION", assigned to the assignee of the present invention. In the '386 request, the base station transmits to the subscriber stations sending frames that include a time multiplexed pilot burst in the frame and are transmitted at a rate based on the channel information transmitted from the subscriber station to

ES 2 398 872 T3 the base station.

A significant difference between voice services and data services is the fact that the former imposes strict and fixed delay requirements. Typically, the overall one-way talk frame delay should be less than 100 ms. Rather, the data delay can become a variable parameter used to optimize the efficiency of the data communication system. Specifically, more efficient error correction coding techniques can be used that require significantly longer delays than can be tolerated by voice services. An exemplary efficient encoding scheme for data is disclosed in United States Patent Application Serial No. 08 / 743,688, entitled "SOFT DECISION OUTPUT DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS," filed November 6, 1996, assigned to the assignee of the present invention.

Another significant difference between voice services and data services is that the former require a common and fixed quality of service (QOS) for all users. Typically, for digital systems providing voice services, this translates into a fixed, equal transmission rate for all users and a tolerable maximum value for speech frame error rates. In contrast, for data services, the QOS may be different from user to user, is negotiable, and should be subject to some fairness restrictions. The QOS that a data communication system provides to a subscriber is typically described by the delay, average throughput, blocking probability, loss of connection probability experienced during service time.

A wireless data communication system can typically provide a range of transmission data rates on both the forward and reverse link. These transmission data rates are assigned to the various active traffic sources according to a strategy, identified as media access control, which must take into account the fact that resources typically offer different input information data rates, essentially depending on the selected data application. Also, the overall system load and channel conditions must be considered when assigning the transmission data rate to a specific subscriber.

Media access control counts for allocating the resource to active subscriber stations on the network in a way that optimizes the tradeoff between overall system throughput, QOS, and algorithm complexity. While in the forward link the “one-to-many” nature of the transmission can be exploited to realize optimal centralized resource allocation at the base station, in the “many-to-one” reverse link the access control strategy optimization problem The middle is complex, and can be solved with a centralized approach at the base station, or with a distributed approach at the subscriber stations. Although many of the techniques described herein can be extended to medium access control of forward link signals, the focus of the present invention is to establish medium access control for the reverse link.

The information that must be used to perform the resource allocation on the reverse link resides both in the base station network and in the subscriber stations. Specifically, on the network side resides the information pertaining to the instantaneous traffic load and reserve capacity of each base station. The load can be quantified for example by increasing the overall received energy on the ground established by the noise power spectral density. The reserve capacity is the difference between the maximum allowable load that avoids network instability and the instantaneous load. At the subscriber station resides information about the class of termination (eg maximum transmission power, transmission buffer size, supported data rate setting), channel conditions (eg signal-to-noise ratio plus interference for all received pilots, transmit power margin), and traffic source status (e.g. buffer status, buffer overflow, average throughput in the past, delay statistics). In principle, the information can be exchanged between the network and the subscribers, but this implies signaling over the air interface which implies a waste of resources and a delay in the decision-making procedure.

A first problem is, therefore, to design a media access control strategy for the reverse link that makes optimal use of the available information by minimizing signaling messages. Also, it is desirable for the media access control strategy to be robust in terms of changes in the class of subscriber station and in the network topology. Another fundamental problem is the allocation of resources for a call transfer subscriber station. In this case, the traffic load and reserve capacity of all base stations involved in the call transfer (identified as base stations in the active set) must be considered, possibly minimizing signaling in the network again. Yet another fundamental problem is the protection of base stations that are not in call transfer with a particular subscriber station, but are nevertheless connected to that subscriber station through an electromagnetic link with path loss comparable to those measured in the active set. These base stations are referred to herein as the candidate set.

Subsequently published application WO 01/08325 discloses a method and apparatus for estimating reverse link load in a wireless communication system comprising transmitting a signal containing negligible energy in a first portion of a reverse link frequency band, measuring in the station

ES 2 398 872 T3 base a first energy in a second portion of the reverse link frequency band, measure a second energy in a second portion of the reverse link frequency band, and calculate the reverse link load using the first and second Energy.

Subsequently published application WO 01/03357 discloses a method and apparatus for determining a reverse link transmission rate in a wireless communication system comprising determining a reverse link transmission rate in accordance with a combined reverse link occupancy signal.

WO 9909779 (A1) entitled "Method And Apparatus For Reverse Link Rate Scheduling discloses multi-level scheduling in a communication system capable of variable speed transmission." Multi-level scheduling is described as improving reverse link utilization and decreasing transmission delay in communication data. Multi-level planning comprises base station level planning, selector level planning (system level) and network level planning. Network level planning is performed by the base station in call handoff with base stations that are controlled by different selector schedulers. Selector level scheduling is performed by remote stations in call handoff with base stations that are controlled by the same selector schedulers and base station level scheduling is performed by remote stations not in call handoff. Base station level planning is performed using residual capacity after higher level planning has been performed. Each planning level can have a different planning interval.

Summary of the invention

The present invention, as set forth in the appended claims, is a new and improved method and apparatus for performing transmission data rate mapping on the reverse link of a high-speed wireless communication network. The speed is determined according to signals indicative of the load conditions of the base stations of the active set of the subscriber station. The base stations react to the action of the subscriber stations by measuring their instantaneous traffic load and providing feedback in the form of slight occupancy tones.

It is an objective of the present invention to optimize access control to the reverse link medium by placing the allocation of the data rate under the control of the subscriber station that has a greater amount of information by which it determines the transmission rate that they do. the elements on the network side. The subscriber has information regarding the amount of information he has lined up to transmit, and the amount of transmit power margin available, the signal-to-noise ratios plus interference in both the active set and the links in the candidate set These are all essential factors in selecting a reverse link transmission speed. Base stations do not have this information in the absence of a significant amount of signaling, which is undesirable.

It is another objective of the present invention to prevent a subscriber station from creating unacceptable interference to candidate base stations by their reverse link transmission, thereby enhancing the protection of the candidate set.

It is another object of the present invention to allow data rate allocation on a packet basis, to provide the flexibility that is necessary to provide efficient service to subscriber stations offering high bursty traffic.

It is another object of the present invention to provide fairness in resource allocation between subscriber stations taking into account the average throughput in the recent past and the possible buffer overflow condition.

It is another object of the present invention to provide efficient reverse link medium access control without requiring any backlink signaling, between base station transceivers and base station controllers, even when the subscriber station is in handoff. call. This is highly desirable because it makes resource allocation independent of network architecture and associated transmission and processing delays.

It is another objective of the present invention to minimize the necessary signaling at the air interface.

It is another objective of the present invention to avoid wasting resources that occurs when the speed used by the subscriber station is lower than the assigned speed. In fact, in closed loop resource allocation the assigned speed and the used speed always coincide.

It is yet another object of the present invention to provide lightweight multi-bit busy tones that indicate not only whether or not a base station is in an overload condition, but also provide some indication of the extent of its load.

ES 2 398 872 T3

Brief description of the drawings

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which similar reference characters are correspondingly identified throughout, and in which:

Figures 1A-1F are flow charts illustrating the speed allocation procedure of the present invention;

Figure 2 is a diagram illustrating the basic elements of the network of the wireless communication system of the present invention;

Figures 3A-3B are block diagrams illustrating the exemplary base station of the present invention;

Figures 4A-4B are raster diagrams illustrating the exemplary forward link framing of the present invention; Y

Figure 5 is a block diagram of the exemplary subscriber station of the present invention.

Detailed description of the preferred embodiments

I. Overview of the procedure

Figure 1A is a flow chart describing the preferred procedure for performing closed loop resource allocation in accordance with the present invention. In the exemplary embodiment, the present invention is employed to determine the data rate of reverse link transmissions from a subscriber station. In block 100, the subscriber station selects an initial desired rate (Vetapa-ι) based on the state of the buffer. Exemplary, the data rate is determined on a packet basis.

Figure 1B is a flow chart describing in more detail speed selection based on buffer state. In block 110, the subscriber station determines the number of bytes in its transmission buffer (Qsize).

In block 112, the subscriber station determines the parameters Vmin and Vmax, Vmin and Vmax, which are the minimum speed and the maximum speed at which the subscriber station is capable of transmitting. Exemplary, Vmax may optionally be set for a particular subscriber station by the serving base station by over-the-air signaling means. An exemplary rate setting (V) in Kbps corresponding to packet sizes (Psize (V)) in bytes of information for those rates is illustrated in Table 1 below.

<td>Speed ​​(V) (kb / s)</td><td> 4,8</td><td> 9,6</td><td> 19,2</td><td> 38,4</td><td> 76,8</td><td> 153,6</td><td> 307,2</td>

<td>Packet size (bytes) (Psize (V))</td><td> 32</td><td> 64</td><td> 128</td><td> 256</td><td> 512</td><td> 1024</td><td> 2048</td>

In control block 114, the subscriber station determines whether the number of bytes of information in the transmission buffer is greater than the packet size for the maximum transmission rate. In the case of exemplary numerology, the maximum speed is 307.2 Kbps and the corresponding maximum packet size is 2048 bytes. If the number of bytes of information in the transmission buffer is greater than the packet size for the maximum transmission rate, then the variable buffer V is set equal to Vmax in block 116. If the number of bytes of information in the transmit buffer is not greater than the packet size for the maximum transmit rate, then in block 118 the variable buffer V is set to the minimum available rate at which it can be used. transmit all the contents of the transmission buffer (Qsize) in a single packet.

In block 119, the subscriber station determines the speed of its last transmission (Vanteior). For example, this value is stored in RAM and overwritten after each transmission. In block 120, a variable temporary speed Vetapa1 is set at the minimum of the speed indicated by V buffer or twice the Vanteior speed.

Exemplary, the subscriber station buffer is separated into two portions. A first portion includes new data for transmission and the second portion includes RLP (Radio Link Protocol) data, which are packets that were previously transmitted but could be retransmitted. Exemplary, a Buffer flag is set when the subscriber station's new data buffer is nearly full. In response to the setting of the buffer nearly full flag, the subscriber station sets its rate selection algorithm. In a first example, the subscriber station adjusts the rate selection algorithm to skew its transmission rate to one of increasing the transmission rate, as will be described in greater detail herein. In an alternative example, the subscriber station transmits at a predetermined higher rate. It will be understood that one of ordinary skill in the art can modify the responses of setting a buffer full flag to increase the transmission rate in a variety of ways that are all within the scope of the present invention. For fairness, you should not set the B buffer flag to more than N buffer times (for

ES 2 398 872 T3 example 25) of the last 100 packets.

Returning to Figure 1, the operation moves to block 102 where the subscriber station determines the maximum speed based on the power margin (V_andcap2) · Figure 1C illustrates the operation performed in step 102 in greater detail. In block 122, the subscriber station determines the maximum transmission power (P_max) in which the subscriber station is capable of operating. For example, the maximum transmission power depends on whether the power amplifier at the subscriber station is mobile or fixed, and on the amount of battery power at the subscriber station if the subscriber station is mobile.

In block 124, the subscriber station calculates a maximum allowed transmission power which is the maximum transmission power P_mmax (dB) determined in step 122 minus a power margin Pmargin (dB), which allows future power level fluctuations to be followed. The subscriber station then sets a variable Vpower equal to the maximum speed, V, that can be reliably transmitted with a power, P (V) (dB), less than the maximum allowable transmit power (P_mmax (dB) - Pmargin (dB)). In block 126, the subscriber station establishes a new V_andta_Pa2 variable equal to the minimum of V_andta_Pai determined in step 100 and V_podetermined in step 124.

Returning to Figure 1A, the procedure next moves to block 104 where the subscriber station determines the maximum transmission rate in accordance with a candidate set protection criterion. The purpose of the rate adjustment in step 104 is to protect the members of the candidate set of the subscriber station that have their reverse links overloaded by subscriber stations that are not in communication with them but are sufficiently visible (in terms of loss of path) to cause interference problems.

Exemplary, the subscriber station is not informed of base station loading problems in the candidate set, because it does not receive the relevant busy tone. Therefore, the candidate set protection algorithm is provided to avoid uncontrolled overloading of the candidate set bas e stations. Exemplary, the amount of reduction in the maximum allowable transmission rate is based on the strength of the pilot signals from the candidate base stations. In particular, the intensity of the pilot signals of the candidate base stations relative to the intensity of the pilot signals of the base stations of the active set.

Figure 1D illustrates the exemplary procedure for determining the maximum transmission rate according to candidate set protection. At block 128, the subscriber station measures the Ec / lo of the pilot signals from each of the base stations in its candidate set that includes all multipath components of the pilot signals from those base stations. At block 130, the subscriber station measures the Ec / lo of the pilot signals from each of the base stations in its active set that includes all multipath components of the pilot signals from those base stations.

In block 132, the subscriber station calculates a metric (Aac) that is a function of the difference in intensity of the signals received by the base stations in the active set and signals received by the base stations in the candidate set. In an exemplary way, the metric (Aac) is set to the difference between the sum of the Ec / lo of all the members of the active set in decibels, and the sum of the Ec / lo of all the members in the candidate set in decibels, as illustrated in equation (1) given below:

<img file="ES2398872T3_D0001.tif" />

(I) where (') // „is the intensity of the i-th pilot of the active set that includes all related multipath components, and E' ^ fi / 1 ^ is the intensity of the j-th pilot in the set candidate that includes all related multipath components.

In a first alternative example, the metric (Aac) is set to the difference between the weakest member of the active set and the strongest member of the candidate set as illustrated in equation (2) given below:

Δ., = Min, {£_c(&lt;) // „(dB)} - max /.(dB)}, (2) where E“ (. I) fl_or is the intensity of the i-th pilot in the active set that includes all related multipath components, and is the intensity of the j-th pilot in the candidate set that includes

ES 2 398 872 T3 all related multipath components.

In a second alternative example, the metric (A_ac) to the difference between the weakest member of the active set and the sum of the members of the candidate set as illustrated in equation (3) given below:

Δ „= τηίη. {Κ“ (dB)} - ^ £; (j) //_or «IB), (3) where E“ (i) / f_tois the intensity of the i-th pilot of the active set that includes all related multipath components, and E⁴(j) //_ORis the intensity of the j-th pilot in the candidate set that includes all related multipath components.

In a third alternative example, the metric (A_ac) to the difference between the member of the highest intensity of the active set and the member of the highest intensity of the candidate set as illustrated in equation (4) given below:

= max_i{£_c^or(i) //_you(dB)} - max / E '(j) / Z₀(dB)}, (4) where is the intensity of the i-th pilot of the active set that includes all related multipath components, and ^ rOV ^ is the intensity of the j-th pilot in the candidate set that includes all components related multipath.

A fourth alternate example calculates the metric based on the selection of the pilot in the active set that drives the power control algorithm.

Other methods of determining the metric will be apparent to one of ordinary skill in the art and are within the scope of the present invention.

At block 134, a V is set_dog variable at maximum rate (V) so that the difference between the power required to transmit a packet from the subscriber station at rate V, P (V) (dB), minus a protection factor, exceeds the metric value calculated (A_ac). For example, the protection factor is determined as the power in decibels required to transmit at a speed that is equal to N_prot times V_m¡_n, where_prot is an integer scale factor and V_m¡N is the minimum rate at which the subscriber station is capable of transmitting.

At block 136, a V is determined_andta_Pa3 variable, which is the speed set after performing the candidate set protection operation, selecting the minimum speed of V_andta_Pa2, or V_ACn

Returning to Figure 1A, at block 106, the subscriber station selects the maximum busy tone from those received from all base stations in the active set. In a simple case, where the busy tone is a single bit indicative of the reverse link capacity load condition or the existence of additional reverse link capacity, the selection of the maximum busy tone is simply a matter of OR operation. to all received busy tones. If any of the busy tones indicate a capacity loading condition, the subscriber station stochastically slows down its transmissions, as described below. If all busy tones indicate additional reverse link capacity, then the subscriber station stochastically increases its transmission rate, as described below.

Exemplary, the busy tone is a multi-bit software busy tone, designated with two bits (b1, b2) corresponding to the meanings in Table 2 below.

Table 2

<td>(b1, b2)</td><td>Meaning</td>

<td> (0,0)</td><td>Base Station Lightly Charged</td>

<td> (0,1)</td><td>Stable Base Station</td>

<td> (1,0)</td><td>Highly Charged Base Station</td>

ES 2 398 872 T3 (continued)

<td>(b1, b2)</td><td>Meaning</td>

<td> (1,1)</td><td>Base Station Overloaded</td>

Figure 1E illustrates an exemplary procedure for determining the values ​​of the two busy tone bits. At block 138, the base station estimates its reverse link load. There are a plurality of methods for estimating reverse link load all of which are applicable to the present invention. The example for estimating reverse link loading is described in detail in US Patent Application Serial No. 09 / 204,616, entitled "Method and Apparatus for Loading Estimation", which is assigned to the assignee of the present invention.

In block 140, the base station compares the estimated reverse link load to a first threshold value (TH1). If the estimated reverse link load is less than the threshold value TH1, it is then determined that the base station reverse link is poorly loaded and in block 142, the busy tone bits are set to (0,0) . If the estimated reverse link load is greater than or equal to TH1 the operation then moves to block 144.

In block 144, the base station compares the estimated reverse link load to a second threshold value (TH2). If the estimated reverse link load is less than the threshold value TH2, it is then determined that the reverse link of the base station is stable and in block 146, the busy tone bits are set to (0,1). If the estimated reverse link load is greater than or equal to TH2 then the operation moves to block 148.

At block 148, the base station compares the estimated reverse link load to a third threshold value (TH3). If the estimated reverse link load is less than the threshold value TH3, it is then determined that the base station reverse link is highly loaded and in block 150, the busy tone bits are set to (1,0) . If the estimated reverse link load is greater than or equal to TH3 then move the operation to block 152. In block 152, the base station is determined to be overloaded and busy tones are set to (1,1).

All threshold competitions can be implemented through hysteresis loops to avoid too frequent crossover.

In block 106, the subscriber station receives the busy tones from all base stations in their active set and selects the highest busy tone.

In block 108, the transmission rate for the current packet is selected according to the maximum occupancy tone (b1, b2) selected in step 106. Figure 1F illustrates the speed selection procedure based on the maximum tone of selected occupation.

In control block 154, the subscriber station determines if the maximum busy tone (bi, b2) has the value (0,0), which would indicate that all base stations in the active set are lightly loaded. In this case, deterministic speed increase is possible; the operation moves to control block 156, and the packet transmission rate is set to V_andcap3 · If the maximum occupancy tone does not have the value (0,0), the operation moves to control block 158.

In control block 158, the subscriber station determines whether the maximum busy tone (bi, b₂) has the value (0,1), which would indicate that at least one base station in its active set is stable (but not poorly charged). If the maximum occupancy tone has the value (0,1), the operation moves to control block 160, where stochastic speed increase is possible. In control block 160, the subscriber station determines whether the calculated rate V_andta_Pa3 is less than or equal to V_anter¡or If the V_andta_Pa3 is less than or equal to V_anther, then at block 162 the current packet is transmitted at rate V_andta_Pa3 Si V_andta_Pa3 is greater than V_anThen at block 164 the current packet is transmitted at a stochastically determined rate so that the packet is transmitted at rate V_andt_aPa3 with probability po is transmitted at speed V_anterior with probability 1-p. If the maximum busy tone does not have the value (0,1), the operation moves to control block 166.

In the example, the probability (p) of increasing the transmission rate of the subscriber station is determined according to the previous activity of the subscriber station and on the near-full flag of the buffer (Bbuffer). In particular, in the example, the probability is determined according to the average speed used in a predetermined number of previous packets, V_med¡a · In the example, the probability is determined according to the equation:

p = minj 1,1 + B Memory / 2. /?

intermediateI ntax °^{§ 2} R

N speeds (5) 'measured

ES 2 398 872 T3 where B buffer is the full buffer flag which in the example assumes a value of zero or one where one unites the full buffer condition, Vmax as described above is the maximum transmission speed of the subscriber station, Nspeeds is the number of speeds available to the subscriber station.

In control block 166, the subscriber station determines if the maximum busy tone (bi, b2) has the value (1.0), which would indicate that at least one base station in its active set is highly loaded. If the maximum occupancy tone has the value (1.0), the operation moves to control block 168, in which stochastic speed reduction is necessary. In control block 168, the subscriber station determines if the calculated speed Vetapa3 is less than Vanterior. If Vetapa3 is less than Vanterior, the current packet at Vetapa3 speed is then transmitted in block 170. If Vetapa3 is greater than or equal to Vanterior, then in block 172 the current packet is transmitted at a stochastically determined speed so that the packet is transmitted at Vanterior speed with probability p or it is transmitted at the higher of Vanterior / 2 or Vmin with probability 1-p. In the example, the number p is recalculated according to equation (5).

If the maximum busy tone does not have the value (1.0), the operation moves to block 174 indicating that at least one base station in the active set of the subscriber station is in an overload condition. In block 176, it is determined that the transmission rate of the current packet is greater than Vanterior / 2 or Vmin.

II. Network description

Referring to the figures, Figure 2 depicts the exemplary data communication system of the present invention comprising multiple cells 200a-200f. Each cell 200 is served by a corresponding base station 202 or base station 204. Base stations 202 are base stations that are in active communication with subscriber station 206 and are said to make up the active set of subscriber station 206. Base stations 204 are not in communication with subscriber station 206 but have signals strong enough to be controlled by subscriber station 206 to be added to the active set if received signals increase in intensity due to a change in path characteristics. of propagation. Base stations 204 are said to make up the candidate set of subscriber station 206.

In the example, subscriber station 206 receives data information from at least one base station 202 on the forward link at each time slot, but receives busy tone information from all base stations in the active set. Also, the subscriber station communicates with all base stations in set 202 active on the reverse link. If the number of active base stations is more than one, the subscriber station 206 is in call transfer. Subscriber stations 206, especially those located near a cell boundary, can receive the pilot signals from multiple base stations 204 in the candidate set. If the pilot signal is above a predetermined threshold, subscriber station 206 may request that base station 204 be added to the active set of subscriber station 206. In the example, before the candidate base station 204 is added to the active set, there is typically no way for the subscriber station to control its busy tone. If a way is provided to control the busy tone of a candidate base station, then this busy tone enters the set within which a maximum is selected according to step 106 described above.

III. Direct link structure

A block diagram of the exemplary forward link architecture of the present invention is shown in Figure 3A. The data is subdivided into data packets and provided to a CRC encoder 312. For each data packet, the encoder 312 generates frame check bits (eg, the CRC parity bits) and inserts the code tail bits. The 312 CRC encoder formatted packet comprises the data, frame check, and code tail bits and other overhead bits described below. The formatted packet is provided to encoder 314 which, in the example, encodes the data according to a convolutional or turbo encoding format. The encoded packet is provided from encoder 314 to interleaver 316 which reorders the code symbols in the packet. The interleaved packet is provided to frame scoring element 318 which removes a fraction of the packet in the manner described below. The dotted packet is provided to multiplier 320 which scrambles the data with the scrambling sequence from scrambler 322. The output of multiplier 320 comprises the scrambled packet.

The scrambled packet is provided to variable rate controller 330 which demultiplexes the packet into K parallel and quadrature infase channels, where K is data rate dependent. In the example, first the scrambled packet is demultiplexed into infase (I) and quadrature (C) flows. In the example, stream I comprises even indexed symbols and stream C comprises odd indexed symbols.

Each stream is further demutiplexed into K parallel channels so that the symbol rate of each channel is fixed for all data rates. The K channels of each stream are provided to the Walsh cover element 332 which covers each channel with a Walsh function to provide orthogonal channels. The orthogonal channel data is provided to the gain element 334 which scales the data to maintain a constant total energy per segment (and therefore constant output power) for all speeds of

ES 2 398 872 T3 data. The scaled data from gain element 334 is provided to multiplexer 360 (MUX) which multiplexes the data with a preamble sequence. The output of MUX 360 is provided to multiplexer 362 (MUX) which multiplexes the traffic data, power control bits, and pilot data. The output of the MUX 362 comprises the Walsh I channels and the Walsh C channels.

Reverse link power control (RPC) bits are provided to symbol repeater 350 which repeats each RPC bit a predetermined number of times. The reptilian RPC bits are provided to the Walsh cover element 352 which covers the bits with the Walsh covers that correspond to the RPC indices. The covered bits are provided to gain element 354 which scales the bits prior to modulation to maintain a constant total transmit power.

In addition, a direct activity bit is provided to the symbol repeater 350. The forward activity bit alerts subscriber station 106 of an upcoming blank frame in which the base station will not transmit forward link data. This transmission is done to allow the subscriber station 106 to make a better estimate of the C / I of the signal from the base stations 102. The repeated versions of the forward activity bit are covered by Walsh in the Walsh cover element 352 to be orthogonal to the Walsh covered power control bits. The covered bits are provided to gain element 354 which scales the bits prior to modulation to maintain a constant total transmit power.

In addition, a busy tone is provided to the symbol repeater 350. The busy tone alerts subscriber station 206 of a reverse link loading condition. In one example, the busy tone is a single bit indicative that the reverse link is fully loaded or has spare capacity. In a further example, the busy tone is a two-bit signal indicative of a request by base stations 202 for subscriber stations 206 in their coverage area to deterministically increase or decrease the rate of their reverse link transmissions, or to stochastically increase or decrease the speed of your reverse link transmissions. The repeated versions of the busy tone are covered by Walsh in the Walsh cover element 352 to be orthogonal to the power control bits covered by Walsh and the direct activity bit. The covered bit is provided to gain element 354 which scales the bits prior to modulation to maintain constant total transmit power.

The pilot data comprises a sequence of all zeros (or all ones) that is provided to multiplier 356. Multiplier 356 covers the pilot data with the Walsh Wo code. Since the Walsh Wo code is a sequence of all zeros, the output of multiplier 356 is the pilot data. Pilot data is time multiplexed by MUX 362 and provided to Walsh channel I which is spread by PNi code in complex multiplexer 366 (see Figure 3B). Exemplary, the pilot data is not spread by the long PN code, which is disabled during the pilot burst by MUX 376, to allow reception by all subscriber stations 376. The pilot signal is therefore an unmodulated BPSK signal.

A block diagram of the exemplary modulator used to modulate the data is illustrated in Figure 3B. The Walsh channels I and Walsh channels C are provided to the adders 364a and 364b, respectively, which add the K Walsh channels to provide the signals l_ITSmy C_ITSm, respectively. The signals are provided_ITSmy C_ITSm to the multiplier 366 of complexes. Complex multiplier 366 also receives PN_I and PN_C signals from multipliers 378a and 378b, respectively, and multiplies the two complex inputs according to the following equation:

<img file="ES2398872T3_D0002.tif" />

where L_muit and C_muit are the outputs of the multiplier 366 of complexes and j is the representation of complexes. The signals are provided_muit and Qmuit to filters 368a and 368b, respectively, which filter the signals. The filtered signals from filters 368a and 368b are provided to multipliers 370a and 370b, respectively, which multiply the signals with the sinusoidal in-phase COS (w_ct) and the quadrature sinusoid SIN (w_ct), respectively. The modulated I and modulated Q signals are provided to the adder 372 which adds the signals to provide the direct modulated wavelength S (t).

Exemplary, the data packet is spread with the long PN code and the short PN codes. The long PN code scrambles the packets so that only the subscriber station 106 for which the packet is intended can descramble the packets. Exemplary, the pilot and power control bits and control channel packets are spread with the short PN codes but not with the long PN code to allow all subscriber stations 106 to receive these bits. The long PN sequence is generated by long code generator 374 and provided to multiplexer 376 (MUX). The long PN mask determines the offset of the long PN sequence and is assigned only to the destination subscriber station 106. The output of the MUX 376 is the long PN sequence during the data portion of the transmission and zero otherwise (eg, during the pilot and power control portion). The activated long PN sequence is provided

ES 2 398 872 T3 from MUX 376 and the short PNi and PNq sequences from the short code generator 380 to multipliers 378a and 378b, respectively, which multiply the two sets of sequences to form the PN_I and PN_C signals, respectively. The PN_I and PN_C signals are provided to complex multiplier 366.

The exemplary traffic channel block diagram shown in Figures 3A and 3B is one of many architectures that support data coding and modulation on the forward link. Other architectures, such as the architecture for the forward link traffic channel in the CDMA system that corresponds to the IS-95 standard, can also be used and are within the scope of the present invention.

IV. Frame structure of the forward link

An exemplary forward link frame structure diagram of the present invention is illustrated in Figure 4A. The transmission of the traffic channel is subdivided into frames which, exemplary, are defined as the length of the short PN sequences or 26.67 ms. Each frame may carry control channel information addressed to all subscriber stations 106 (control channel frame), traffic data routed to a particular subscriber station 106 (traffic frame), or may be empty (idle frame). . The content of each frame is determined by scheduling performed by the transmitting base station 102. Exemplary, each frame comprises 16 time slots, each time slot having a duration of 1.667 ms. A time slot of 1.667 is adequate to enable the subscriber station 106 to perform the C / I measurement of the forward link signal. A time interval of 1,667 ms also represents a sufficient amount of time for efficient packet data transmission.

For example, each forward link data packet comprises 1024 or 2048 bits. Therefore, the number of time slots required to transmit each data packet depends on the data rate and ranges from 16 time slots for a rate of 38.4 Kbps to 1 time slot for a rate of 1.2288. Mbps.

An exemplary diagram of the forward link slot structure of the present invention is shown in Figure 4B. Exemplary, each slot comprises three of the four time multiplexed channels, the traffic channel, the control channel, the pilot channel, and the overhead control channel. Exemplary, the pilot signal is transmitted in two bursts and the overhead control channel is transmitted on either side of the second pilot burst. Traffic data is carried in three portions of the interval (402a, 402b and 402c).

The first pilot burst 406a is time multiplexed in the first half of the slot by multiplexer 362. The second pilot burst 406b is time multiplexed in the second half of the slot. On either side of the second pilot burst 406b, the overhead channel data 408 including the forward activity bit, busy tones, and power control bits in the slot is multiplexed.

Exemplary, the busy tone is a two-bit signal, and the busy tone is set only once per frame. Exemplary, the busy tone is sandwiched between the slots of a frame such that the even slots carry the first bit of the busy tone and the odd slots carry the second bit of the busy tone. Other ways to interleave the busy tone bits will be obvious to those skilled in the art and are within the scope of the present invention.

V. Subscriber station architecture

Figure 5 illustrates the exemplary subscriber station of the present invention. Buffer 524 provides a signal indicative of the amount of data queued for transmission to rate allocation control processor 522. The rate allocation control processor 522 selects the rate based on the state of the buffer memory as described with respect to step 100 above. Exemplary, buffer 524 is divided into two parts. A first part of buffer 524 stores new data for transmission. A second part of buffer 524 stores data for retransmission. Exemplary, the rate control processor 522 selects the rate in accordance with a full buffer flag that is set in accordance with the new data to be transmitted.

Transmitter 528 is responsible for upscaling, filtering, and amplifying the reverse link signal for transmission. Transmitter 528 provides a signal to rate allocation control processor 522 indicative of the amount of power margin available for transmission of the current data packet. In response to this signal the rate allocation control processor 522 determines the setting for the transmission rate of the next packet as described with respect to block 102 above.

Forward link signals are received by subscriber station 206 at antenna 500 and provided through duplexer 502 to receiver 504. Receiver 504 downconverts, filters and amplifies the received signal, and provides the signal to calculator 506 pilot power. The pilot energy calculator 506 calculates the energy of the pilot signals received from base stations 202 of the active set and base stations 204 of the candidate set.

The received signals are provided to pilot de-spreader 510, which de-spreads the pilot signals from

ES 2 398 872 T3 according to control signals from the search controller 508. Exemplary, paging controller 508 provides a PN offset of a quantity set or active base station set to pilot de-spreader 510 which in response de-spreads the pilot signal from a candidate set base station 204 or active set base station 206 .

The despread pilot symbols are provided to the square element 512 which calculates the energy of the symbols and provides the symbol energy values ​​to the accumulator 514. The accumulator 514 accumulates the energies over the time interval of the pilot burst and provides the energy of pilot burst for speed assignment element 522. In response to the pilot burst energies of the quantity set base stations (Ec / Io) and the active set base station pilot burst energies (Ea / Io), the rate assignment control processor 522 calculates the protection setting of the candidate set for the selected speed as described with respect to block 104 above.

The received signals are also provided to the busy tone demodulators 516. The busy tone demodulators 516 demodulate the busy tone values ​​for each base station 202 in the active set and provide the busy tone values ​​for each base station to the rate assignment control processor 522. In response the rate assignment control processor 522 selects a maximum busy tone as described in 106 above, and calculates the transmission speed as described with respect to 108 above.

Once the transmission speed has been determined by the speed allocation control processor 522, a signal indicative of the selected speed is provided to the buffer 524, modulator 526 and transmitter 528. The buffer 524 outputs a block of data according to the selected baud rate to modulator 526. Modulator 526 modulates the signal in accordance with the selected data rate and provides the modulated data to transmitter 528. The transmitter amplifies the signal in accordance with the selected transmission rate and provides the signal through duplexer 502 for transmission over antenna 500. The selected speed can be indicated to active base stations via a reverse link message.

The above description of the preferred embodiments is provided to enable one skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments.