Candidate system search and soft handoff between frequencies in a multi-carrier mobile communication system

ES 2 380 072 T3

DESCRIPTION

Search for candidate system and smooth transfer between frequencies in a multi-carrier mobile communication system

Background of the invention

I. Field of the invention

The present invention relates generally to mobile communication systems. More specifically, the present invention relates to mobile communication systems in which mobile stations can receive and demodulate signals transmitted on more than one frequency.

II. Description of Related Art

Figure 1 shows a general block diagram of a previous mobile station 100 used in a cellular telephone system, such as a code division multiple access (CDMA) cellular telephone system. US Patent No. 5,109,390, which has been assigned to the assignee of the present invention and which is incorporated herein by reference, discloses a schematic diagram of an example of a CDA cellular telephone system and a block diagram of a mobile station used in such a system. Referring to Figure 1, mobile station 100 comprises an antenna 105 for communicating with base stations, a transmitter 110 for transmitting signals from mobile station 100, a receiver 120 for receiving signals, a pager and demodulator unit 130, and a duplexer 115 coupled to antenna 105, transmitter 110, and receiver 120 to properly route outgoing signals from transmitter 110 to antenna 105 and incoming signals from antenna 105 to receiver 120. The duplexer 115 is a conventional duplexer that can be a full duplexer, which allows signals to be transmitted and received simultaneously, or a half-duplexer, which at any given time allows only the transmission or reception of signals.

Receiver 120 comprises a first band pass filter (FPB) 121 coupled to duplexer 115, a mixer 122 coupled to first FPB 121, a local oscillator (OL) 123 coupled to mixer 122, a second FPB 124 coupled to mixer 122, and a sub-receiver 125 coupled to the second FPB 124. The sub-receiver 125 includes a frequency translator 126, which may be a digital or analog frequency translator, and a third FPB 127.

Duplexer 115 routes the incoming signals to the first FPB 121, which, in turn, sends a pass-through version of the incoming signals to mixer 122. Mixer 122 also receives a second input from OL 123. The output of mixer 122 is sent to second FP B 124, which sends to sub-receiver 125 a band-pass version of its input signal. The frequency translator 126 receives the output of the second FPB 124 and shifts the received signal in the frequency domain, such that its output is centered around a desired frequency, specifically the frequency at which the signals are carried when they are transmitted. between mobile station 100 and a base station with which mobile station 100 is in communication. The third FPB 127 receives the output of the frequency translator 126 and outputs a version of its input passed by band. The third FPB 127 has a 1.25 MHz bandpass and is centered around the frequency at which signals are carried when they are transmitted between mobile station 100 and the base station that mobile station 100 is in. communication. The output of the third FPB 127 is transmitted to the searcher and demodulator unit 130. The demodulators in the searcher and demodulator unit 130 demodulate the incoming waveform signals. The demodulation correlators of the demodulators then extract from the demodulated signals the codes of a communications code channel, such as Walsh codes and pseudo-noise (PR) codes, and combine the extracted codes. The searchers in the searcher and demodulator unit 130 look for the existence of a structured waveform, such as codes from a communications code channel, eg, Walsh codes or PR codes. Examples of seekers and demodulators are disclosed in US Patents No.^you 5,103,459, 5,490,165 and 5,506,865, all of which have been assigned to the assignee of the present invention and are incorporated herein by reference. It should be noted that in some of the patents referenced above, a digital receiver or a digital data receiver may refer to a demodulator or a combination of a finder and one or more demodulators. Similarly, an analog receiver may refer to what is referred to in the present application as receiver 120 or an equivalent thereof.

Since the sub-receiver is tuned to only one frequency at any given time, the mobile station can only be in communication with a base station that transmits signals in the frequency range to which the mobile station is tuned. This limitation with respect to the frequency to which the mobile station is tuned causes the mobile station and the wireless communication system within which the mobile station operates to suffer from several disadvantages. First, the mobile station cannot be in soft handoff between two different frequencies. Second, the mobile station cannot monitor or search for pilots on more than one frequency at any given time. Third, in the idle state, the mobile station cannot monitor or search for pages on more than one frequency at any given time.

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Summary of the invention

The present invention overcomes the aforementioned disadvantage by providing a mobile station, a wireless communication system and a method as set forth in the appended claims. Each of the sub-receivers in the mobile station of the present invention can be independently tuned to a particular frequency. As a consequence of having multiple sub-receivers that can be independently tuned to different frequencies, the mobile station of the present invention can simultaneously receive signals on more than one frequency from different base stations or from different sectors of a base station. This allows the mobile station (1) to be (a) in soft handoff between two different frequencies that are received from different base stations or (b) in smoother handoff between two different frequencies that are received from different sectors of the same base station or (c) in smoother soft handoff between multiple frequencies being received from different base stations, where, in the case of at least one base station, multiple frequencies are received from different sectors of the same base station, which is (2) in communication with at least one base station at a first frequency while simultaneously searching and monitoring pilots at other frequencies with little or no degradation , to the uplink or downlink with the base station with which it is in communication, and (3) simultaneously search and monitor pages on more than one frequency in the idle state, that is, when the mobile station is not on a traffic channel.

In one embodiment, the receiver comprises two subreceptors. In a first two sub-receiver embodiment, the first sub-receiver has a frequency band that is twice as wide in the frequency domain as the frequency band of the second sub-receiver. In a second embodiment of two sub-receivers, the first sub-receiver has a frequency band that is three times wider in the frequency domain than the frequency band of the second sub-receiver.

Brief description of the drawings

Figure 1 is a general block diagram of a previous mobile station.

Figure 2 is a general block diagram of the mobile station of the present invention.

Figure 3 is a graph in the frequency domain of multiple frequencies and multiple code channels used to transmit signals in the wireless communication system of the present invention.

Figure 4 is a more detailed view of code channels used to transmit signals on one of the frequency bands of Figure 3.

Figures 5-10 are tables showing examples of different combinations of frequencies, base stations, code channels, and code symbols used in the wireless communication system of the present invention.

Figure 11 is a general block diagram of one embodiment of the multi-sub-receiver mobile station of the present invention.

Detailed description of the preferred embodiment

Figure 2 shows a general block diagram of the mobile station of the presently preferred embodiment of the invention. Mobile station 200 comprises elements contained in mobile station 100. For each element of mobile station 200 that has a corresponding element in mobile station 100, a reference number has been selected by adding 100 to the reference number of the corresponding element of the mobile station 100. For example, the mobile station duplexer is referred to as duplexer 215, where 215 is the sum of 100 and reference number 115 of the duplexer 115 of mobile station 100. Since elements of mobile station 200 that have corresponding elements in mobile station 100 are well known to those skilled in the art and have been described above, those elements of mobile station 200 will no longer be described herein. document to allow concentrating on the inventive features of the mobile station 200 of the present invention. Similarly, other elements commonly used in mobile stations have been omitted from the block diagrams of mobile stations 100 and 200, since such elements are well known to those skilled in the art.

As can be seen in Figures 1 and 2, mobile station 200 contains elements in addition to those that have corresponding elements in mobile station 100. For example, unlike receiver 120, in mobile station 100, which has only one sub-receiver 125 , receiver 220 of mobile station 200 comprises N sub-receivers 225, with N being an integer greater than one. Each of the N sub-receivers 225 can be independently tuned to a different frequency to search, monitor and demodulate signals sent on different frequencies. The use of multiple sub-receivers that can be independently tuned to different frequencies allows mobile station 200 to simultaneously receive signals on more than one frequency from different base stations or from different sectors of a base station.

In some embodiments, the searcher and demodulator unit 230 may contain additional demodulator FPBs (not shown) to further filter signals received from the FPBs 227 from receiver 220. A demodulator would include demodulator FPBs when the bandwidth of the FPB 227 from which the demodulator receives signals is wide enough to contain more than one frequency band in which the signals 3

ES 2 380 072 T3 are commonly transmitted in a wireless communication system. In a wireless communication system, in accordance with the presently preferred embodiment of the invention, a 1.25 MHz frequency band is commonly used to transmit signals. Therefore, when more than one 1.25 MHz band can fit in the power FPB 227 frequency band, the number of 1.25 MHz bands that can fit in the power FPB 227 frequency band determines the number of demodulator FPBs that should be used in a demodulator that receives signals from the feed FPB 227. It should be noted that the above procedure for determining the number of demodulator FPBs to be used in a demodulator can be applied to systems that use a frequency band other than a 1.25 MHz band to transmit signals. For such systems, the frequency band commonly used in those systems, rather than a 1.25 MHz band, will be used to determine the number of demodulator FPBs (not shown) to be used in the demodulator.

In one embodiment, N equals three, in which case mobile station 200 comprises three sub-receivers. In an embodiment that has three sub-receivers, each of the sub-receivers is tuned to a different frequency and filters signals within a bandwidth of approximately 1.25 MHz. In this embodiment, the demodulators do not need to have any demodulator FPBs, since the bandwidth of each FPB 227 is equal to that of the frequency bands in which signals are commonly transmitted in a wireless communication system. .

In a second embodiment, mobile station 200 comprises two sub-receivers. In a first embodiment of a two sub-receiver mobile station, one sub-receiver filters signals with a bandwidth of approximately 3.75 MHz, while the other sub-receiver filters signals with a bandwidth of approximately 1.25 MHz. In the first embodiment mentioned above where the FPB 227 of a sub-receiver has a bandwidth of approximately 3.75 MHz, the demodulator coupled to the 3.75 MHz FPB 227 includes three demodulator FPBs (not shown) to subdivide the signals. received from the 3.75 MHz FPB 227 on three separate signals, each of which is in one of three adjacent bands having a bandwidth of approximately 1.25 MHz. In one embodiment, the band for the 1.25 MHz FPB 227 may correspond to one of the three 1.25 MHz subbands of the 3.75 MHz FPB 227. In such an embodiment, the 3.75 MHz FPB 227 and 1.25 MHz FPB 227 together include three demodulator FPBs (not shown) to subdivide received signals from the 3.75 MHz FPB 227 and the 1.25 MHz FPB 227. MHz into three separate signals, each of which is in one of three adjacent bands that have a bandwidth of approximately 1.25 MHz. In a second embodiment of a two-sub-receiver mobile station, one sub-receiver filters signals with a bandwidth of approximately 2.5 MHz, while the other sub-receiver filters signals with a bandwidth of approximately 1.25 MHz. In the aforementioned second embodiment in which the FPB 227 of a sub-receiver has a bandwidth of approximately 2.5 MHz, the demodulator coupled to the 2.5 MHz FPB 227 includes two demodulator FPBs (not shown) to subdivide the signals. received from the 2.5 MHz FPB 227 on two separate signals, each of which is in one of two adjacent bands having a bandwidth of approximately 1.25 MHz.

In one embodiment, FPBs 227 may comprise surface acoustic wave (SAW) filters, which are well known to those of skill in the art. It should be noted that the FPBs used in the present invention are not limited to SAW filters, but may instead be any FPBs used in the art, such as other types of analog filters (e.g., element filters cascading agglomerates, crystals) or digital filters (for example, finite impulse response (FIR) filters).

Figure 11 is a general block diagram of one embodiment of the multi-sub-receiver mobile station of the present invention. In the mobile station 1100 of FIG. 11, each of the analog-to-digital converters (CAD) 1125, either alone or in combination with a digital signal processor 1129, can be envisioned as a sub-receiver of receiver 1120. Thus, for example, the nth CAD 1125 or the nth CAD 1125 in combination with the PSD 1129 can be understood to be the nth subreceptor. Although in the embodiment shown in Figure 11 there is a single PSD 1129 corresponding to all CAD 1125, in an alternative embodiment it is conceivable that each CAD 1125 would be associated with a separate corresponding PSD that is not shared with other CAD 1125s.

Each CAD 1125 can be independently tuned to sample a portion of the frequency band of the incoming signal in digital signals. Thus, the first CAD 1125 can be tuned to sample incoming signals of a frequency f1, while the nth CAD 1125 can be tuned to sample incoming signals of a frequency fN, with f1 and fN being different frequencies, and can be the center frequencies for adjacent or non-adjacent frequency bands.

In one embodiment, N equals three, and thus mobile station 1100 comprises three sub-receivers. In an embodiment that has three sub-receivers, each of the sub-receivers is tuned to a different frequency and filters signals within a bandwidth of approximately 1.25 MHz. Mobile station 1100 may also have different combinations of sub-receiver number, sub-receiver bandwidths, and sub-receiver frequencies (in other words, the frequencies each sub-receiver is tuned to) than those described in connection with mobile station 200.

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Additionally, the CAD 1125s can be regular analog-to-digital converters or sigma-delta modulators. The sigma-delta modulator can be a sigma-delta bandpass modulator when the signal is an intermediate frequency (IF) signal or a low-pass signa-delta modulator when the incoming signal is a baseband signal (that is, a signal lower frequency unmodulated). US Patent Application Serial No. 08 / 987,306, filed December 9, 1997, entitled "Receiver With Sigma-Delta Analog-To-Digital Converter," and US Patent Application Serial No. 08 / 928,874, filed on September 12, 1997, entitled "Multi Loop Sigma-Delta Analog-To-Digital Converter", which have been transferred to the assignee of the present invention and which are incorporated herein by reference provide further detail on the sigma-delta modulators that may be used in the present invention.

The PSD 1129 receives digital signals from the CAD 1125. It then band-pass filters each of the signals from the CAD 1125. The PSD 1129 can also mix the input digital signals with the baseband and then use a filter. low-pass, rather than band-pass, to filter digital signals. If the CAD 1125 oversamples the analog signals, in other words, if it samples the analog signals with a frequency greater than the Nyquist frequency or the segment frequency, then the PSD 1129 can also reduce the data from the oversampled data rate to the Nyquist frequency or the frequency of segments. In addition, the PSD 1129 extracts the I (in phase) and Q (quadrature phase) components of the signals. In other words, the signals sent from PSD 1129 to searchers and demodulators 230 are the I and Q components of the input signal. US Patent Application Serial No. 09 / 211,990, filed December 14, 1998, entitled "A Low Current Programmable Digital Filter," which has been transferred to the assignee of the present invention and is incorporated herein for reference, it provides more detail on the aforementioned PSD 1129 functions.

As noted above, the block diagrams of mobile stations 100 and 200 do not show some elements commonly used in mobile stations, since those elements are well known to those skilled in the art. Similarly, the block diagram of mobile station 1100 also does not show some elements commonly used in mobile stations. For example, Figures 1, 2 and 11 do not show a low noise amplifier (LNA) and automatic gain control (AGC), which are commonly used in mobile stations. Those skilled in the art know that an LNA amplifies the signals received from duplexers 115 and 215 before those signals are sent to FPBs 121 and 221, respectively. Similarly, those skilled in the art know that preferably an AGC would control the amplitude of the signals produced by FPBs 124 and 224 before they are sent to sub-receivers 125 and 225 (CAD 1125 in the case of the mobile station 1100). It is also known to those of skill in the art that the AGC setting is controlled based on the signal strength of the signals produced by the subreceptors.

Those skilled in the art will also appreciate that if mobile station 200 frequency translator 226 (or mobile station 100 frequency translator 126) is digital, then the signals received by it are digitized somewhere. along the signal path before being translated into frequency. Similarly, those skilled in the art will realize that if the FPB 227 of the mobile station 200 (or the FPB 127 of the mobile station 100) is analog, then the signal produced by it is converted to a digital signal for its processing by pager and demodulator unit 230 (or pager and demodulator unit 130 in mobile station 100). Similarly, those skilled in the art will appreciate that the receiver (of mobile stations 100 and 200) may include means for extracting the I and Q components of the signals before sending those signals to the demodulator and pager unit.

The ability to simultaneously receive signals on more than one frequency allows the mobile station of the present invention (1) to be (a) in soft handoff between two different frequencies that are received from different base stations or (b) in softer handoff between two different frequencies that are received from different sectors of the same base station or (c) in smoother soft handoff between multiple frequencies that are received from different base stations, in which, in the case of at least one base station, multiple frequencies are received from different sectors of the same base station, which is (2) in communication with at least one base station at a first frequency while , at the same time, searches and monitors pilots at other frequencies with little or no degradation to the up or down links with the base station with which it is in communication, and (3) simultaneously searching and monitoring pages on more than one frequency in the idle state, that is, when the mobile station is not on a traffic channel. In addition, the ability to simultaneously receive signals on more than one frequency allows the mobile station of the present invention to search for signals of different formats and technologies, such as, for example, Advanced Mobile Telephone Service (AMPS), Band AMPS Narrow (NAMPS) and the Global System for Mobile Communications (GSM).

In paging mode, while mobile station 200 (or mobile station 1100) is on a traffic channel, that is, in continuous two-way communication with one or more "anchor" base stations, it can tune in to one or more of its sub-receivers. 225 (or CAD 1125) and one or more of the baseband pagers of the unit 230 of pagers and demodulators at candidate frequencies to look for signals from other base stations or sectors of other base stations, if sectorized antennas are used. As is known in the art, an anchor base station is a base station with which a mobile station is in two-way communication.

ES 2 380 072 T3 continues. Each of the one or more baseband sub-receivers and pagers looking for signals from other base stations can be tuned to one of the candidate base station multi-carrier frequencies to detect the existence of the uplink signal by measuring the power level of the uplink signal for the respective base station and establishing a correlation with the pilot channel, detecting digital control channels of analog cellular systems, or by detecting supplementary link channels. This search helps in the determination of the coverage of the mobile station by different base stations and in the proper synchronization for the handover between frequencies. When the mobile station is performing this search, one or more sub-receivers and their corresponding baseband pagers and demodulators continue to receive the upstream traffic channel. In addition, mobile station 200 (or mobile station 1100) continues to transmit to the base station (s), without interruption, thus ensuring that the downlink functions properly.

During system determination (that is, when the mobile station is determining which wireless communication system it is nearby and with which base station it can communicate), the multiple sub-receivers of the mobile station can be used in parallel to detect uplink signals from multiple base stations. Generally, parallel detection of uplink signals allows faster system determination than sequential (or serial) detection of uplink signals. In an idle state (that is, when the mobile station is not in continuous two-way communication with one or more anchor base stations), the different sub-receivers of the mobile station can be tuned to receive from multiple base stations on the same frequency or per different frequencies to improve the reliability of the radio messaging channel. The mobile station searches for and monitors paging channels from multiple base stations using different portions of its RF input section (ie, sub-receivers) and the baseband demodulator. As the mobile station and its propagation environment change, the relative strengths of these paging channels may vary over time. According to the present invention, the mobile station can monitor one or more paging channels while searching for others. A portion of the mobile station's RF input section can be tuned to a new frequency or frequencies so that the pager (s) can find pilot channels on a new frequency or on different frequencies than those the mobile station is monitoring on that frequency. moment. If strong energy is detected or a high correlation indicates the existence of an uplink signal on the new frequency or frequencies, the mobile station may then choose to monitor the target base station (s), that is, the base station (s). base stations transmitting the pilot channels on the new frequency or frequencies.

Figure 3 is a graph illustrating a representation in the frequency domain of multiple frequencies and multiple code channels used to transmit signals in the present embodiment of the wireless communication system of the invention. In the example shown in Figure 3, there are six different frequencies f1, f2, f3, f4, f5 and f6 used for communication between base stations and mobile stations. In Figure 3, the frequency bands centered around each of f1, f2, f3, f4, f5, and f6 are substantially the same. Also, the frequency bands in which f1, f2, and f3 are centered are adjacent to each other. Similarly, the frequency bands in which f4, f5, and f6 are centered are adjacent to each other. However, the frequency bands in which f3 and f4 are centered are not adjacent to each other. Base station one (EB1) and base station two (EB2) transmit signals at frequencies f1, f2 and f3 using the first and second code channels, respectively. Similarly, base station three (EB3) and base station four (EB4) transmit signals at frequencies f4, f5, and f6 using the third and fourth code channels, respectively. Therefore, as can be seen from the example above, using different code channels, more than one base station can transmit signals on a given frequency. In Figure 3, the signals of the frequencies f1, f4 and f6 shown with a darker outline are destined for a first mobile station, while the signals carried by the frequencies f2, fe and fs are destined for a second mobile station .

Generally, each mobile station can receive code symbols for up to M code channels, M being an integer. More specifically, each demodulation correlate of the mobile station can receive code symbols for up to M code channels. Furthermore, each mobile station can receive code symbols for up to N frequencies, with N being, as indicated above, an integer greater than one representing the number of sub-receivers within the mobile station. N also represents the number of carriers destined for reception by a mobile station within the system. In the example shown in Figure 3, M is at least six and N is equal to three.

Code symbols destined for a target mobile station can be demultiplexed (ie sent as parallel sub-streams) on the six code channels over the three frequencies that carry signals destined for the target mobile station. Some or all of the sub-streams may be duplicated on the six different code channels on the three different frequencies that carry signals destined for the target mobile station. For example, in Figure 3, the code symbols destined for the first mobile station can be demultiplexed or duplicated on the six code channels at frequencies f₃, f4 and f6. Code symbols can also be sent in any combination of demultiplexing and repeating. Some combination of demultiplexing and repeating, an example of which is shown in Figure 10, may be used to avoid interference and attenuation or to balance the load of different carriers and base stations.

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The mobile station multiplexes the demultiplexed symbols while maximally combining the repeated code symbols from different multipath components and different code channels of the carriers it receives. Then, the demultiplexed and combined code symbols are sent to the decoder (not shown) of mobile station 200 (or mobile station 1100).

Some code channels, such as the six code channels of Figure 3, may not carry any code symbols for a target mobile station. For example, some of the six code channels of the fe, f4 and fe frequencies might not carry any code symbols for the first mobile station.

Figure 4 is a more detailed representation of code channels used to transmit signals on one of the illustrative frequency bands of Figure 3. In Figure 4, the illustrative carriers of EB1 and EB2 are at the same frequency and can use the same or different code channels. Code symbols destined for a particular mobile station can be sent by different base stations using different code channels. EB1 uses a code channel 405 and a Walsh channel 410. The EB2 uses three code channels 455, 465 and 475, which are separated by two Walsh channels 460 and 470.

As can be seen from Figure 6, the number of code channels on a carrier used to transmit code symbols to a given mobile station need not equal the number of code channels on other carriers used to transmit code symbols to the same given mobile station. Furthermore, a given carrier may have a higher code symbol frequency than other carriers that are carrying code symbols to the same mobile station on the same or different frequencies. This alleviates the problem of uneven loading on different carriers from the same base station. The ability to send code symbols at different frequencies for each carrier based on channel conditions and the power available on each channel allows improved utilization of channel resources, because transmitting code symbols at the same frequency in all channels would force all channels to be transmitting with the same frequency as the slowest channel in the system, that is, the channel that is least powerful or requires the highest signal-to-noise ratio. One way to allow the transmission of code symbols at different code symbol frequencies on each carrier is to use a demultiplex ratio between different channels that is different from 1 to 1. The demultiplex ratio between two channels refers to the ratio between the transmission frequencies of code symbols on the two channels. In a preferred embodiment, the resulting symbol rate on each carrier is a factor of a frequency of the Walsh function. An alternative approach is to demultiplex the code symbols by taking them out of the cipher directly to the carriers and performing interleaving of the repeated code symbols on each channel separately.

Figures 5-10 are tables showing examples of different combinations of frequencies, base stations, code channels, and code symbols used in the wireless communication system of the present invention.

In Figure 5, the EB1 transmits signals, in this case the code symbols S1 to S12, on the frequencies fe, f₂ and faith. The code symbols S1, S4, S7 and S10 are transmitted by faith, while the code symbols S₂, S5, Sa and S11 are transmitted by f₂, and the code symbols S3, Se, S9 and S12 are transmitted by f3. Thus, the EB1 transmits multiplexed the code symbols S1 to S12 by the consecutive frequencies fe, f₂ and f3.

In the example of Figure 5, the code symbol flow over the uplink remains the same before, during and after the search. Maintaining the same code symbol stream over the uplink results in an effectively increased error correcting coding rate. Code symbols or energy lost due to searching are known to the receiver and are treated as eliminations. Using decision trees and procedures well known to those skilled in the art, depending on the resulting ratio of energy per bit to noise density (Eb / Nt), the attenuation scenario, and the anchor base station's awareness of In searching, the uplink traffic channel power for the mobile station can be increased or otherwise adjusted to ensure that the uplink quality is sufficient.

In another embodiment, the uplink code symbols destined for the mobile station are sent only by the remaining carriers, that is, the carriers that the mobile station continues to demodulate in paging mode.

It should be noted that the above problem of missing code symbols exists when the sub-receivers of the mobile station do not have a combined bandwidth that is sufficient both to receive signals on the frequencies f, f₂ and f3 as for the search frequency. In some embodiments, the code symbols transmitted on the frequencies fe, f₂ and f3 can be received without missing code symbols while searching for signals on another frequency. For example, in the embodiment of the present invention where one sub-receiver has a 3.75 MHz FPB and another sub-receiver has a 1.25 MHz FPB, the sub-receiver with the 3.75 MHz FPB can receive the symbols of code transmitted by frequencies fe, f₂ and f3 while the sub-receiver with the 1.25 MHz FPB searches for signals on another frequency. In such a case, the code symbols for the frequencies fe, f₂ and f3 would not be missed at the mobile station due to searching by the sub-receiver with the 1.25 MHz FPB. Alternatively, a 1.25 MHz sub-band of the 3.75 MHz FPB can be used to search while 7 are used

ES 2 380 072 T3 its two remaining 1.25 MHz sub-bands and the 1.25 MHz FPB to receive code symbols on frequencies f1, f2 and f3.

In Figure 6, EB1 transmits the code symbols on f and f2 using code channels C1 and C2. EB1 transmits code symbols S1, S4, S7 and S10 on f using code channel C1. EB1 also transmits code symbols S2, S5, Sa and S11 on f using code channel C2. EB1 also transmits code symbols S3, Se, S9 and S12 on f2 using code channel C1. Code channels C1 and C2 can be Walsh code channels.

In Figure 6, the EB1 uses only two frequencies f and f2, instead of three frequencies T, f2 and f3 as in the example shown in Figure 5, to transmit the code symbols S1 to S12. However, EB1, in the example of Figure 6, uses two, instead of a Walsh code channel as in the example shown in Figure 5, for the T frequency. The use of more Walsh code channels allows the EB1, in the example of Figure 6, to transmit code symbols with the same frequency as in the example of Figure 5. Thus, the throughput of code symbols can be maintained using a higher frequency of symbols per carrier, such as by using more Walsh code channels per carrier. The throughput of code symbols can also be reduced, resulting in higher error-correcting code frequency and less redundancy.

A code symbol distribution such as the example shown in Figure 6, in which only two frequencies are used to transmit code symbols to the mobile station on the uplink, allows a mobile station that can simultaneously receive signals over the only three frequencies receive code symbols on the uplink without losing code symbols due to searching for a third frequency. For example, while sub-receivers tuned to frequencies f and f2 receive code symbols on the uplink, the sub-receiver tuned to frequency f3 can be used to search for signals from other base stations or from different sectors of the same base station if used sectorized antennas.

A code symbol distribution such as that shown in Figure 6 can also be used when the load on the frequency f3 from EB1 is relatively high and that on the frequency f is relatively low.

In Figure 7, the EB1 transmits the code symbols S1, S4, S7 and S10 by T, the code symbols S2, S5, Sa and S11 by f2, and the code symbols S3, Sa, S9 and S12 by f3 while EB2 transmits code symbols S2, S5, Sa and S11 on f1. In the example in Figure 7, some of the multiplexed code symbols, specifically the S2, S5, Sa and S11 code symbols, are sent by both EB1 and EB2 by f2 and T, respectively, for greater reliability. at the cost of redundancy, since EB2 does not send additional information to that sent by EB1. Such redundancy for the sake of greater reliability may be particularly appropriate in a situation where there is a smooth handover between EB1 and EB2 at two different frequencies f2 and f1.

In Figure 8, the EB1 transmits the code symbols S1, S4, S7 and S10 by T, the code symbols S2, S5, Sa and S11 by f2, and the code symbols S3, S6, S9 and S12 by f3 while EB2 transmits the code symbols S1, S4, S7 and S10 on f1, the code symbols S2, S5, Sa and S11 on f2, and the code symbols S3, S6, S9 and S12 on f3. In the example in Figure a, there is a total redundancy in the code symbols transmitted by EB1 and EB2, since the code symbols transmitted by EB1 by T, f2 and f3 are also transmitted by EB2 by them. frequencies. This greater redundancy results in greater reliability.

In Figure 9, the EB1 transmits the code symbols S1, S7, S13 and S19 by T, the code symbols S2, Sa, S14 and S20 by f2, and the code symbols S3, S9, S15 and S21 by f3 while the EB3 transmits the code symbols S4, S10, S16 and S22 on f1, the code symbols S5, S11, S17 and S23 on f2, and the code symbols S6, S12, S1B and S24 on f3. In the example of Figure 9, there is neither redundancy nor the resulting higher reliability, since the code symbols are demultiplexed on frequencies from different base stations for the sake of higher throughput.

In Figure 10, EB1 transmits code symbols S1, S4, S7 and S10 on T, EB2 transmits code symbols S1, S4, S7 and S10 on T, EB3 transmits code symbols S2, S5. Sa and S1 on f4 and the code symbols S3, S6, S9 and S12 on f6, and the EB4 transmits the code symbols S2, S5, Sa and S11 on f4 and the code symbols S3, S6, S9 and S12 on f6. In the example of Figure 10, the code symbols are demultiplexed at different frequencies, but more than one base station transmits the same code symbols for each frequency to avoid interference and attenuation. In the example in Figure 10, there is smooth transfer between BE1 and BE2 at frequency T. Similarly, there is smooth frequency between BE3 and BE4 at frequencies f4 and f6.

Although the present invention has been described in particular with respect to the illustrated embodiments, it will be appreciated that various alterations, modifications, and adaptations may be made based on the present disclosure and are intended to be within the scope of the present invention. Although the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to the disclosed embodiments, but rather is intended covering various modifications and equivalent provisions included within the scope of the appended claims.

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