HK1112120A

HK1112120A - Hybrid orthogonal frequency division multiple access system and method

Info

Publication number: HK1112120A
Application number: HK08106793.8A
Authority: HK
Inventors: 张国栋; 蔡寅铭; 潘俊霖
Original assignee: 美商内数位科技公司
Priority date: 2005-04-22
Filing date: 2006-04-20
Publication date: 2008-08-22

Description

Hybrid ofdma systems and methods

Technical Field

The present invention relates to wireless communication systems. More particularly, the present invention relates to a hybrid ofdma system and method.

Background

Future wireless communication systems will be expected to provide broadband services like wireless internet access to users. Such broadband services require reliable and high throughput transmission over a wireless channel, which is typically time dispersive and frequency selective. The wireless channel is limited by limiting spectrum and Internal Symbol Interference (ISI) caused by multipath fading. Orthogonal Frequency Division Multiplexing (OFDM) and orthogonal frequency division code division multiple access (OFDMA) are the most promising solutions for next generation wireless communication networks.

Ofdm has high spectral efficiency because the subcarriers used in the ofdm system overlap in frequency, allowing a suitable Modulation and Coding Scheme (MCS) to be utilized throughout the subcarriers. In addition, the performance of ofdm is simple because the baseband modulation and demodulation can be performed using simple Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT) operations. Other advantages of the ofdm scheme include a simple receiver structure and excellent robustness in multipath environments.

Ofdma has been adopted by many wireless/wireline communication system standards such as Digital Audio Broadcasting (DAB), land-based digital audio broadcasting (DAB-T), IEEE 802.11a/G, IEEE 802.16, Asynchronous Digital Subscriber Line (ADSL), and is considered for adoption in the long-term evolution of the third generation partnership project (3GPP) (LTE), the development of code division multiple access 2000(CDMA 2000), the fourth generation (4G) wireless communication system, IEEE 802.11n, and so on.

The main problem of ofdma is that it is difficult to eliminate or control inter-cell interference to achieve a frequency reuse factor of one. Frequency hopping between cells in cooperation with subcarrier allocation has been proposed to eliminate inter-cell interference. However, the efficiency of both methods is limited.

Disclosure of Invention

The present invention relates to a hybrid Orthogonal Frequency Division Multiple Access (OFDMA) system and method. The system includes a transmitter and a receiver. The transmitter includes a first spread ofdma subassembly, a first non-spread ofdma subassembly and a first common subassembly. The first spread ofdma subassembly spreads the input data and maps the spread data to a first group of subcarriers. The first non-spread OFDMA subassembly maps input data to a second group of subcarriers. The first common subassembly transmits input data mapped to the first and second groups of subcarriers using ofdma. The receiver includes a second spread ofdma subassembly, a second non-spread ofdma subassembly and a second common subassembly. The second common subassembly processes received data using ofdma to recover data mapped to the subcarriers. The second spread ofdma subassembly recovers the first input data by spreading user data in the code domain, and the second non-spread ofdma subassembly recovers the second input data.

Drawings

Figure 1 is a block diagram of an exemplary hybrid Orthogonal Frequency Division Multiple Access (OFDMA) system configured in accordance with the present invention.

Fig. 2 shows an example of frequency domain spreading and subcarrier mapping in accordance with the present invention.

Fig. 3 shows another example of spreading and subcarrier mapping in accordance with the present invention.

Fig. 4 shows an example of subcarrier time-frequency hopping according to the present invention.

Fig. 5 is a block diagram of an exemplary time-frequency rake combiner configured in accordance with the present invention.

Detailed Description

The terms "transmitter" and "receiver" hereinafter encompass, but are not limited to, a User Equipment (UE), a Wireless Transmit Receive Unit (WTRU), a mobile station, a fixed or mobile subscriber unit, a pager, a node-B, a base station, a location controller, an access point, or any other type of device capable of operating in a wireless environment.

The features of the present invention may be combined in an Integrated Circuit (IC) or be configured in a circuit comprising a multitude of interconnecting elements.

The present invention may be applied to any wireless communication system utilizing orthogonal frequency division code division multiple access (or ofdma) and/or Code Division Multiple Access (CDMA), such as IEEE 802.11, IEEE 802.16, third generation (3G) cellular systems, fourth generation (4G) systems, satellite communication systems, and the like.

Fig. 1 is a block diagram of an exemplary hybrid ofdma system 10 including a transmitter 100 and a receiver 200 in accordance with the present invention. The transmitter 100 includes a spread ofdma subassembly 130, a non-spread ofdma subassembly 140, and a common subassembly 150. In the spread ofdma subassembly 130, input data 101 (for one or more users) is spread with a spreading code to produce a plurality of chips 103, and the chips 103 are then mapped to subcarriers. In the non-spread ofdma subassembly 140, the input bits 111 (for one or more users) are mapped to subcarriers without spreading.

The spread ofdma subassembly 130 includes a spreader 102 and a first subcarrier spread mapping unit 104. The non-spread ofdma subassembly 140 includes a serial-to-serial (S/P) converter 112 and a second subcarrier mapping unit 114. The common subcomponent 150 includes an N-point Inverse Discrete Fourier Transform (IDFT) processor 122, a sequence-to-serial (P/S) converter 124 and a Cyclic Prefix (CP) insertion unit 126.

Assuming that there are N subcarriers in the system and that K different users are communicating in the system at the same time, among K users, data is transmitted to K through the spread OFDMA subassembly 130_SAnd (4) a user. The number of subcarriers used in the spread OFDMA subassembly 130 and the non-spread OFDMA subassembly 140 is N_SAnd N_O。N_SAnd N_OThe numerical value of (A) satisfies 0. ltoreq.N_S≤N、0≤N_ON and N are not more than_S+N_OThe condition of less than or equal to N.

The input data 101 is spread by the spreader 102 into a plurality of chips 103. The chip 103 is mapped to the N by the sub-carrier expansion mapping unit 104_SAnd (4) sub-carriers. The spreading may be in the time domain, frequency domain or inTo be executed in both. For a particular user, the spreading factors in the time domain and the frequency domain are SF, respectively_tAnd SF_f. The joint spreading factor for the user is SF_jointWhich is equal to SF_t×SF_f. When SF_tWhen 1, the spreading is performed only in the frequency domain, whereas when SF_fWhen 1, the expansion is performed only in the opportunity domain. The frequency domain spreading for user i is then assigned to the number N of subcarriers for that user i_S(i) The limit of (2). The allocation of the subcarriers may be static or dynamic. At N for each user i_S(i)＝N_SIn this case, the spread ofdma becomes an ofdma.

In the spread ofdma subassembly 130, one subcarrier may be mapped to more than one user. In this case, the input data 101 of two or more users mapped to the same subcarrier becomes code multiplexed and should therefore be spread with different spreading codes. If spreading is performed in both the time and frequency domains, the spreading codes assigned to users in the time domain and the frequency domain, or both, are different.

Fig. 2 shows an example of frequency domain spreading and subcarrier mapping in accordance with the present invention. The input data 101 is multiplexed by a multiplexer 202 with a spreading code 204 to generate a plurality of chips 103'. The chip 103' is converted to a serial chip 103 by a serial to serial converter 206. Each of the serial chips 103 is then mapped to one of the subcarriers by the subcarrier mapping unit 104 before being sent to the idft processor 122.

Fig. 3 shows another example of frequency domain spreading and subcarrier mapping in accordance with the present invention. Instead of spreading the code by a spreader, it uses a repeater 302 to repeat each input data 101 multiple times at a chip rate to generate chips 103'. The chip 103' is then converted to a serial chip 103 by a serial to serial converter 304. Each of the serial chips 103 is then mapped to one of the subcarriers by the subcarrier mapping unit 104 before being sent to the idft processor 122.

Alternatively, each input data is spread by a spreader to generate a plurality of chip streams, which are then mapped to subcarriers, as the input data is spread in the time domain. In this case, the time domain spreading can also be performed by simply repeating the input data without using a spreading code.

The common pilot may be transmitted on the subcarriers used in the spread ofdma subassembly 130. The coaching can also be spread out for discrimination from other user data.

Referring again to fig. 1, in the non-spread ofdma subassembly 140, the input bits 111 of different users are converted into serial bits 113 by the serializer 112. The subcarrier mapping unit 114 allocates users to one or more subcarriers so that at most one user uses each subcarrier and the bits from each user are mapped by the subcarrier mapping unit to the subcarriers allocated to that user. In the sub-method, the user is multitasking in the frequency domain. The number of sub-carriers allocated to user i is denoted as N_O(i) And 0 is not more than N_O(i)≤N_O. The subcarrier allocation may be static or dynamic.

According to the present invention, the non-spread ofdma subassembly 140 may perform time-frequency hopping in a pseudo-random manner in each cell. By time domain hopping, the users transmitting in a cell change over time (in other words, in terms of one or more ofdm symbols or frames). The subcarriers allocated to users in a cell for transmission are hopped at each or a number of ofdm symbols or frames by frequency domain hopping. In this way, inter-cell interference between the user and the cell can be eliminated and averaged.

Fig. 4 illustrates a time-frequency hopping example using 10 subcarriers s0-s9 during the time period T0-T6 in accordance with the present invention. As an example, in fig. 2 subcarriers s3, s5, s8 are used for spread ofdma, and the remaining subcarriers are used for non-spread ofdma. For subcarriers allocated to non-spread ofdma, the subcarriers allocated to the users and the time period hop in a pseudo-random manner. For example, data for user 1 is transmitted at T0 through s9, at T1 through s7, at T3 through s7, at T4 through s1 and s9, while data for user 2 is transmitted at T0 through s4, at T1 through s6, at T2 through s3, at T4 through s0 and s 4. Thus, it transmits data to different users via different ofdm symbols or frames and eliminates inter-cell interference.

Referring again to FIG. 1, the chip 105 and the data 115 are provided to the inverse discrete Fourier transform processor 122. The inverse discrete Fourier transform processor 122 transforms the chip 105 and the data 115 into time domain data 123. The inverse discrete Fourier transform processor 122 may be implemented using an Inverse Fast Fourier Transform (IFFT) or equivalent operation. The time domain data 123 is then converted to serial data 125 by the serializer 124. A cyclic prefix, also known as a Guard Period (GP), is then added to the serial data 125 by the cyclic prefix insertion unit 126. Data 127 can then be transmitted over the wireless channel 160.

The receiver 200 includes a spread ofdma subassembly 230, a non-spread ofdma subassembly 240, and a common subassembly 250 for ofdma. The common subcomponent 250 includes a cyclic prefix removal unit 202, a deserializer 204, an N-point Discrete Fourier Transform (DFT) processor 206, an equalizer 208, and a subcarrier demapping unit 210. The spread ofdma subassembly 230 includes a code domain user separation unit 214 and the non-spread ofdma subassembly 240 includes a serializer 216.

The receiver 200 receives data 201 transmitted over the channel. The cyclic prefix removal unit 202 removes a cyclic prefix from the received data 201. After cyclic prefix removal, data 203, which is time domain data, is converted to sequence data 205 by the serializer 204. The sequence data 205 is provided to the discrete fourier transform processor 206 for conversion into frequency domain data 207, which means N sequence data over N subcarriers. The discrete Fourier transform may be performed by a fast Fourier transform or equivalent operation. The frequency domain data 207 is provided to the equalizer 208 and data equalization is performed on each subcarrier. As in conventional ofdm systems, a simple one-tap equalizer may be used.

After equalization for each subcarrier, the data corresponding to a particular user is separated by the subcarrier demapping unit 210, which is a reverse operation performed by the subcarrier demapping units 104, 114 at the transmitter 100. In the non-spread ofdma subassembly 240, the serializer 216 simply converts each user data 211 to serial data 217. In the spread ofdma subassembly 230, the data 212 on the separated subcarriers is further processed by the code domain user separation unit 214. Based on the spreading done at the transmitter 100, a corresponding user separation is performed in the code domain user separation unit 214. For example, if the spreading is performed only in the time domain at the transmitter 100, a conventional rake combiner can be used as the code domain user separation unit 214. If the spreading is performed only in the frequency domain at the transmitter 100, a conventional (frequency domain) despreader can be used as the code domain user separation unit 214. If spreading is performed in both the time domain and the frequency domain at the transmitter 100, a time-frequency rake combiner can be used as the code domain user separation unit 214.

Fig. 5 is a block diagram of an exemplary time-frequency rake combiner 500 configured in accordance with the present invention. The exemplary time-frequency rake combiner 500 performs processing in both the time and frequency domains to recover data spread in both the time and frequency domains at the transmitter 100. It should be noted that the time-frequency rake combiner 500 may also be implemented in different ways, and the configuration provided in fig. 5 is only an example and not a limitation, and the aspects of the present invention are not limited to the structure shown in fig. 5.

The time-frequency rake combiner 500 includes a despreader 502 and a rake combiner 504. For a particular user, the data 212 separated and collected by the subcarrier demapping unit 210 in fig. 1 for spreading out the ofdma subassembly 230 is delivered to the despreader 502. The despreader 502 performs frequency-sequence domain despreading of the data 212 over the subcarriers. The despreader 502 includes a plurality of multiplexers 506 for multiplexing the despread code conjugates 508 of the data 212, a summer 512 for summing the multiplication outputs 510, and a normalizer 516 for normalizing the summed outputs 514. The despread output 518 is then processed by the rake combiner 504 to recover the user's data by time domain combining.

Referring again to fig. 1, the transmitter 100, the receiver 200, or both may include multiple antennas and hybrid ofdma according to the present invention may be performed using multiple antennas at the transmitter side, the receiver side, or both.

Examples

1. A hybrid Orthogonal Frequency Division Multiple Access (OFDMA) system includes a transmitter and a receiver. The transmitter includes a first spread ofdma subassembly for spreading a first input data of a first user group and mapping the spread data to a first subcarrier group; a first non-spread ofdma subassembly for mapping the second input data to a second group of subcarriers; and a first common subassembly for transmitting the first and second input data mapped to the first and second subcarrier groups using orthogonal frequency division code division multiple access. The receiver includes a second common subassembly for processing the received data using hybrid ofdma to recover data mapped to the subcarriers; a second spread OFDMA subassembly for recovering the first input data; and a second non-spread OFDMA subassembly for recovering the second input data.

2. The system of embodiment 1 wherein the first spread ofdma subassembly spreads the first input data in at least one of a time domain and a frequency domain.

3. The system of embodiment 2 wherein the first spread ofdma subassembly spreads the first input data by repeating the first input data at a chip rate.

4. The system as in any embodiments 1-3, wherein the first spread OFDMA subassembly and the first non-spread OFDMA subassembly dynamically map the subcarriers.

5. The system as in any embodiments 1-4, wherein the first spread OFDMA subassembly transmits common pilot over the first group of subcarriers.

6. The system as in any embodiments 1-5, wherein the first non-spread OFDMA subassembly performs at least one of time-domain hopping and frequency-domain hopping in mapping the second input data to the second group of subcarriers.

7. The system as in any embodiments 1-6, wherein the second spread OFDMA subassembly of the receiver comprises a rake combiner.

8. The system as in any embodiments 1-7, wherein the second ofdma subassembly of the receiver comprises a time-frequency rake combiner.

9. The system as in any embodiments 1-8, wherein at least one of the transmitter and the receiver comprises multiple antennas.

10. A hybrid Orthogonal Frequency Division Multiple Access (OFDMA) system includes a transmitter and a receiver. The transmitter comprises a spreader for spreading first input data of a first user group to generate a chip; a first subcarrier mapping unit for mapping the chip to a first subcarrier group; a first serial to serial (S/P) converter for converting second input data of a second user group into first serial data; a second subcarrier mapping unit for mapping the first sequence data to the second group of subcarriers; an Inverse Discrete Fourier Transform (IDFT) processor for performing IDFT on the outputs of the first and second sub-carrier mapping units to generate time domain data; a first serial-to-serial (P/S) converter for converting the time domain data into serial data; and a Cyclic Prefix (CP) inserting unit for inserting a CP into the serial data for transmission. The receiver includes a cyclic prefix removal unit for removing a cyclic prefix from received data; a second serializer/deserializer for converting the output of the cp removal unit into second serial data; a Discrete Fourier Transform (DFT) processor for performing DFT on the second sequence data to generate frequency domain data; an equalizer for performing equalization on the frequency domain data; a subcarrier demapping unit which separates the frequency domain data after equalization of the first user group and the second user group; a code domain user separation unit for separating the frequency domain data after equalization of the first user group in a code domain to recover the first data; and a second serializer to deserializer converting the frequency domain data into serial data after equalization of the second group of users to recover the second input data.

11. The system of embodiment 10 wherein the spreader spreads the first input data in at least one of a time domain and a frequency domain.

12. The system of embodiment 11 wherein the spreader spreads the first input data by repeating the first input data at a chip rate.

13. The system as in any embodiments 10-12, wherein the first subcarrier mapping unit and the second subcarrier mapping unit dynamically map the subcarriers.

14. The system as in any embodiments 10-13, wherein the transmitter transmits common pilots on the first group of subcarriers.

15. The system as in any embodiments 10-14, wherein the second subcarrier mapping unit performs at least one of time domain hopping and frequency domain hopping in mapping the second input data to the second group of subcarriers.

16. The system as in any embodiments 10-15, wherein the code domain user separation unit comprises a rake combiner.

17. A system as in any of embodiments 10-16 wherein the code domain user separation unit comprises a time-frequency rake combiner.

18. The system as in any embodiments 10-17, wherein at least one of the transmitter and the receiver comprises multiple antennas.

19. A method for transmitting data using hybrid Orthogonal Frequency Division Multiple Access (OFDMA), wherein, at a transmitter, first input data of a first user group is spread to generate chips; mapping the chip to a first group of subcarriers; converting second input data of a second user group into first sequence data; mapping the first sequence data to a second group of subcarriers; performing an Inverse Discrete Fourier Transform (IDFT) on the data outputs mapped to the first and second subcarrier groups to generate a time domain data; converting the time domain data into serial data; inserting a Cyclic Prefix (CP) into the serial data; and transmitting the cyclic prefix insertion data; and, at a receiver, receiving data transmitted by the transmitter; removing a cyclic prefix from the received data; converting the cyclic prefix removed data into second sequence data; performing a Discrete Fourier Transform (DFT) on the second sequence data to generate frequency domain data; performing equalization on the frequency domain data; separating the frequency domain data after equalization of the first group of users and the second group of users; separating the data of the first user group in a code domain to recover the first data; and converting the data of the second user group into serial data to recover second input data.

20. The method of embodiment 19 wherein the spreading of the first input data is performed in at least one of a time domain and a frequency domain.

21. The method of embodiment 20 wherein the spreading of the first input data is performed by repeating the first input data at a chip rate.

22. The method as in any embodiments 19-21, wherein the first group of subcarriers and the second group of subcarriers are mapped dynamically.

23. The method as in any embodiments 19-22, further comprising the transmitter transmitting common pilots on the first group of subcarriers.

24. The method as in any embodiments 19-23, wherein at least one of time domain hopping and frequency domain hopping is performed in mapping the first sequence data to the second group of subcarriers.

25. The method as in any embodiments 19-24, wherein separating the data of the first group of users in a code domain is performed using a rake combiner.

26. A method as in any embodiments 19-25 wherein separating data for a first group of users in a code domain is performed using a time-frequency rake combiner.

Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the present invention or in various combinations with or without other features and elements of the present invention.

Claims

1. A hybrid orthogonal frequency division code division multiple access (OFDMA) system comprising:

a transmitter, comprising:

a first spread ofdma subassembly for spreading a first input data of a first user group and mapping the spread data to a first subcarrier group;

a first non-spread ofdma subassembly for mapping the second input data to a second group of subcarriers; and

a first common subcomponent for transmitting the first input data and second data mapped to the first subcarrier group and second subcarrier group using orthogonal frequency division code division multiple access; and

a receiver, comprising:

a second common subcomponent for processing the received data using hybrid ofdma to recover the data mapped to the subcarrier;

a second spread OFDMA subassembly for recovering the first input data; and

a second non-spread OFDMA subassembly for recovering the second input data.

2. The system of claim 1 wherein the first spread ofdma subassembly spreads the first input data in at least one of a time domain and a frequency domain.

3. The system of claim 2 wherein the first spread ofdma subassembly spreads the first input data by repeating the first input data at a chip rate.

4. The system of claim 1 wherein the first spread ofdma subassembly and the first non-spread ofdma subassembly dynamically map the subcarriers.

5. The system of claim 1 wherein the first spread ofdma subassembly transmits common pilot on the first group of subcarriers.

6. The system of claim 1 wherein the first non-spread ofdma subassembly performs at least one of time domain hopping and frequency domain hopping in mapping the second input data to the second group of subcarriers.

7. The system of claim 1 wherein the second spread ofdma subassembly of the receiver comprises a rake combiner.

8. The system of claim 1 wherein the second ofdma subassembly of the receiver comprises a time-frequency rake combiner.

9. The system of claim 1 wherein at least one of the transmitter and the receiver includes multiple antennas.

10. A hybrid Orthogonal Frequency Division Multiple Access (OFDMA) system, comprising:

a transmitter, comprising:

the expander is used for expanding first input data of a first user group to generate a chip;

a first subcarrier mapping unit for mapping the chip to a first subcarrier group;

a first serial to serial (S/P) converter for converting second input data of a second user group into first serial data;

a second subcarrier mapping unit for mapping the first sequence data to the second group of subcarriers;

an Inverse Discrete Fourier Transform (IDFT) processor for performing IDFT on the outputs of the first and second sub-carrier mapping units to generate time domain data;

a first serial-to-serial (P/S) converter for converting the time domain data into serial data; and

a Cyclic Prefix (CP) inserting unit for inserting a CP into the serial data for transmission; and

a receiver, comprising:

a cyclic prefix removal unit for removing a cyclic prefix from the received data;

a second serializer/deserializer for converting the output of the cp removal unit into second serial data;

a Discrete Fourier Transform (DFT) processor for performing DFT on the second sequence data to generate frequency domain data;

an equalizer for performing equalization on the frequency domain data;

a subcarrier demapping unit which separates the frequency domain data after equalization of the first user group and the second user group;

a code domain user separation unit for separating the frequency domain data after equalization of the first user group in a code domain to recover the first data; and

a second serializer to deserializer converts the frequency domain data into serial data after equalization of the second group of users to recover the second input data.

11. The system of claim 10 wherein the spreader spreads the first input data in at least one of a time domain and a frequency domain.

12. The system of claim 11, wherein the spreader spreads the first input data by repeating the first input data at a chip rate.

13. The system of claim 10 wherein the first subcarrier mapping unit and the second subcarrier mapping unit dynamically map the subcarriers.

14. The system of claim 10 wherein the transmitter transmits common pilot on the first group of subcarriers.

15. The system of claim 10 wherein the second subcarrier mapping unit performs at least one of time domain hopping and frequency domain hopping in mapping the second input data to the second group of subcarriers.

16. The system of claim 10 wherein the code domain user separation unit comprises a rake combiner.

17. The system of claim 10 wherein the code domain user separation unit comprises a time-frequency rake combiner.

18. The system of claim 10 wherein at least one of the transmitter and the receiver includes multiple antennas.

19. A method for transmitting data using hybrid Orthogonal Frequency Division Multiple Access (OFDMA), the method comprising:

at a transmitter

Expanding first input data of a first user group to generate a chip;

mapping the chip to a first group of subcarriers;

converting second input data of a second user group into first sequence data;

mapping the first sequence data to a second group of subcarriers;

performing an Inverse Discrete Fourier Transform (IDFT) on the data outputs mapped to the first and second subcarrier groups to generate a time domain data;

converting the time domain data into serial data;

inserting a Cyclic Prefix (CP) into the serial data; and

transmitting the cyclic prefix insertion data; and

at a receiver

Receiving data transmitted by the transmitter;

removing a cyclic prefix from the received data;

converting the cyclic prefix removed data into second sequence data;

performing a Discrete Fourier Transform (DFT) on the second sequence data to generate frequency domain data;

performing equalization on the frequency domain data;

separating the frequency domain data after equalization of the first group of users and the second group of users;

separating the data of the first user group in a code domain to recover the first data; and

the data of the second user group is converted into serial data to recover second input data.

20. The method of claim 19 wherein the spreading of the first input data is performed in at least one of a time domain and a frequency domain.

21. The method of claim 20 wherein the spreading of the first input data is performed by repeating the first input data at a chip rate.

22. The method of claim 19 wherein the first group of subcarriers and the second group of subcarriers are mapped dynamically.

23. The method of claim 19 further comprising the transmitter transmitting common pilots on the first group of subcarriers.

24. The method of claim 19 wherein at least one of time domain hopping and frequency domain hopping is performed in mapping the first sequence data to the second group of subcarriers.

25. The method of claim 19 wherein separating the data of the first group of users in a code domain is performed using a rake combiner.

26. The method of claim 19 wherein separating the data for the first group of users in a code domain is performed using a time-frequency rake combiner.