KR101302411B1 - Hybrid orthogonal frequency division multiple access system and method - Google Patents

Abstract

A hybrid orthogonal frequency division multiple access (OFDMA) system comprising a transmitter and a receiver is disclosed. The transmitter includes a first spread OFDMA subassembly, a first non-spread OFDMA subassembly, and a first common subassembly. The first spreading OFDMA subassembly spreads the input data and maps the spread data to the first subcarrier group. The first non-spread OFDMA subassembly maps the input data to the second subcarrier group. The first common subassembly transmits input data mapped to the first and second subcarrier groups 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 the received data to recover data mapped to the subcarrier using OFDMA. The second spread OFDMA subassembly separates user data in the code domain to recover the first input data and the second non-spread OFDMA subassembly recovers the second input data.

Description

Hybrid Orthogonal Frequency Division Multiple Access System and Method {HYBRID ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM AND METHOD}

The present invention relates to a wireless communication system. More specifically, the present invention relates to a hybrid orthogonal frequency division multiple access (OFDMA) system and method.

Future wireless communication systems are expected to provide broadband services such as wireless Internet access to subscribers. Such broadband services require reliable and high throughput transmission over time-distributed and frequency selective radio channels. However, the radio channel is subject to inter-symbol interference (ISI) caused by multipath fading and the spectrum is limited. Orthogonal Frequency Division Multiplexing (OFDM) and OFDMA are one of the most promising solutions for next generation wireless communication systems.

OFDM has high spectral efficiency because the subcarriers used in the OFDM system are frequency overlapped and an adaptive modulation and coding scheme (MCS) is adopted for the subcarriers. In addition, in the implementation of OFDM, baseband modulation and demodulation are very simple because they are performed by simple Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT) operations. Other advantages of OFDM include the simplicity of the receiver structure and the robustness in a multipath environment.

OFDM and OFDMA are Digital Audio Broadcast (DAB), Terrestrial Digital Audio Broadcast (DAB-T: Digital Audio Broadcast Terrestrial), IEEE 802.11a / g, IEEE 802.16, Asymmetric Digital Subscriber (ADSL) It is being adopted by several wireless / wired communication standards such as Line, and will be adopted by 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), CDMA 2000 Evolution, 4th Generation (4G) Wireless Communication System, IEEE 802.11n, etc. It is considered.

One important problem inherent to OFDM and OFDMA is that it is difficult to mitigate or control intercell interference to achieve frequency reuse factor 1. Subcarrier allocation coordination and frequency hopping have been proposed between cells to mitigate intercell interference. However, the effectiveness of these methods is limited.

The present invention relates to a hybrid 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 spreading OFDMA subassembly spreads the input data and maps the spread data to the first subcarrier group. The first non-spread OFDMA subassembly maps the input data to the second subcarrier group. The first common subassembly transmits input data mapped to the first subcarrier group and the second subcarrier group 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 of the receiver processes the received data to recover the data mapped to the subcarrier using OFDMA. The second spread OFDMA subassembly separates user data from the code domain to recover first input data, and the second non-spread OFDMA subassembly recovers second input data.

The present invention provides a hybrid orthogonal frequency division multiple access (OFDMA) system and method that facilitates mitigating or controlling intercell interference.

1 is a block diagram of an exemplary hybrid OFDMA system constructed in accordance with the present invention.
2 illustrates an example of frequency domain spreading and subcarrier mapping according to the present invention;
3 illustrates another example of frequency domain spreading and subcarrier mapping according to the present invention;
4 illustrates an example of time-frequency hopping of a subcarrier in accordance with the present invention.
5 is a block diagram of an exemplary time-frequency rake combiner constructed in accordance with the present invention.

Hereinafter, the terms "transmitter" and "receiver" refer to user equipment (UE), wireless transmit / receive unit (WTRU), mobile station, fixed or mobile subscriber unit, pager, node B, base station, site controller. And other types of devices capable of operating in an access point or wireless environment.

Features of the present invention may be organized into integrated circuits (ICs) or composed of circuits including a plurality of interconnecting components.

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes OFDMA (or OFDM) and / or Code Division Multiple Access (CDMA), such as IEEEE 802.11, IEEE 802.16, 3rd generation (3G) cellular systems, 4G systems, satellite communications systems, and the like. It can be applied to a wireless communication system.

1 is a block diagram of an exemplary hybrid OFDMA system 10 that includes 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, the input data 101 (for one or more users) is spread by a spreading code to generate a plurality of chips 103, which are then mapped to subcarriers. do. In non-spread OFDMA subassembly 140, input bits 111 (for one or more different users) are mapped to subcarriers without spreading.

The spread OFDMA assembly 130 includes a spreader 102 and a first subcarrier mapping unit 104. The non-spread OFDMA subassembly 140 includes a series-parallel (S / P) converter 112 and a second subcarrier mapping unit 114. The common subassembly 150 includes an N point inverse discrete Fourier transform (IDFT) processor 112, a parallel-serial (P / S) converter 124, and a cyclic prefix (CP) insertion unit 126. do.

When there are N subcarriers in the system and K different users are communicating at the same time in the system, data for the K _S users among the K users is transmitted through the spread OFDMA subassembly 130. The number of subcarriers used for the spread OFDMA subassembly 130 and the non-spread OFDMA subassembly 140 is N _S and N _O, respectively. The value of N _S N _O and shall meet the condition of 0 ≤N _S ≤N, 0≤N _O ≤N, and N _S + N _O ≤N.

The input data 101 is diffused into the plurality of chips 103 by the diffuser 102. Chip 103 is mapped to the N _S subcarriers by the subcarrier mapping unit 104. Spreading can be in the time domain or in the frequency domain or in both domains. For a particular user, spreading factors in time domain and frequency domain are denoted by SF _t and SF _f , respectively. The _joint diffusion factor for that user is denoted by the SF _joint , which is equal to SF _t × SF _f . When SF _t = 1, spreading is performed only in the frequency domain, and when SF _f = 1, spreading is performed only in the time domain. The frequency domain spread for user i is limited to the number of subcarriers assigned to user i, ie N _S (i). The assignment of subcarriers can be static or dynamic. For all users i, if N _S (i) = N _S , then spread OFDMA becomes spread OFDM.

One subcarrier may be mapped to a plurality of users in the spread OFDMA subassembly 130. In this case, since the input data 101 of two or more users mapped to the same subcarrier is code multiplexed, it must be spread using different spreading codes. If spreading occurs in both time and frequency domains, then the spreading code assigned to the user may be different in either the time domain or the frequency domain, or in both domains.

2 shows an example of frequency domain spreading and subcarrier mapping according to the present invention. Input data 101 is multiplied by spreader 204 by multiplier 202 to produce a plurality of chips 103 '. This chip 103 'is converted into a parallel chip 103 by the S / P converter 206. Each parallel chip 103 is then mapped to one of the subcarriers by the subcarrier mapping unit 104 before being sent to the IDFT processor 122.

3 shows another example of frequency domain spreading and subcarrier mapping according to the present invention. Instead of multiplying the spreading code in the spreader, iterator 302 may be used to iterate each input data 101 multiple times at a chip rate to generate chip 103 '. Then, the chip 103 'is converted into the parallel chip 103 by the S / P converter 304. Each parallel chip 103 is mapped to one of the subcarriers by the subcarrier mapping unit 104 before being sent to the IDFT processor 122.

Alternatively, when input data is spread in the time domain, each input data is spread by a spreader to produce a plurality of chip streams, which are mapped to subcarriers. In this case, time domain spreading can also be performed by simple iteration of the input data without using a spreading code.

The common pilot may be transmitted on the subcarriers used in spread OFDMA subassembly 130. To distinguish it from other user data, common pilots are also spread.

Referring back to FIG. 1, in the non-spread OFDMA subassembly 140, input bits 111 of different users are converted into parallel bits 113 by the S / P converter 112. The subcarrier mapping unit 114 assigns a user to one or more subcarriers so that each subcarrier is used by at most one user and bits from each user are mapped to subcarriers assigned to that user by the subcarrier mapping unit. In this way, users are multiplexed in the frequency domain. The number of subcarriers assigned to user i is denoted by N _O (i), where ₀ ≦ N _O (i) ≦ N _O. The assignment of subcarriers can be static or dynamic.

According to the present invention, time-frequency hopping may be pseudorandom in each cell with respect to the non-spread OFDMA subassembly 140. With time domain hopping, the user transmitting in a cell changes from time to time (ie, over one or several OFDM symbols or frames). With frequency domain hopping, subcarriers assigned to users transmitting in one cell are hopped for one or several OFDM symbols or frames. In this way, intercell interference can be mitigated and averaged between the user and the cell.

4 shows an example of time-frequency hopping when 10 subcarriers, s0-s9, are used during the time interval of T0-T6 according to the present invention. For example, in FIG. 2, subcarriers s3, s5, and s8 are used for spread OFDMA, and the remaining subcarriers are used for non-spread OFDMA. In the case of subcarriers allocated to non-spread OFDMA, the subcarriers and time intervals allocated to the user hop pseudorandomly. For example, user 1's data is sent through T0 to s9, T1 to s7, T3 to s7, T4 to s1 and s9, and user 2's data to T0 to s4, T1 to s6, T2 to s3, T4 to s0 and is sent via s4. Accordingly, data of different users is transmitted through different OFDM symbols or frames, and intercell interference is mitigated.

Referring again to FIG. 1, both the chip 105 and the data 115 are supplied to the IDFT processor 122. The IDFT processor 122 converts the chip 105 and data 115 into time domain data 123. IDFT may be implemented by IFFT or equivalent operation. The time domain data 123 is converted into serial data 125 by the P / S converter 124. Cyclic Prefic (also known as Guard Period (GP)) is added to the serial data 125 by the CP insertion unit 126. Data 127 is then transmitted over wireless channel 160.

Receiver 200 includes a spread OFDMA subassembly 230, a non-spread OFDMA subassembly 240, and a common subassembly 250 for hybrid OFDMA. The common subassembly 250 includes a CP removal unit 202, a P / S converter 204, an N point Discrete Fourier Transform (DFT) processor 206, an equalizer 208, and subcarrier demapping. Unit 210. Spread OFDMA subassembly 230 includes code domain user separation unit 214 and non-spread OFDMA subassembly 240 includes P / S converter 216.

Receiver 200 receives data 201 transmitted over a channel. The CP is removed by the CP removal unit 202 from the received data 201. The data 203 from which the CP has been removed is time domain data and is converted into parallel data 205 by the S / P converter 204. Parallel data 205 is supplied to DFT processor 206 and converted into frequency domain data 207, which means N parallel data on N subcarriers. DFT can be implemented by FFT or equivalent operation. Frequency domain data 207 is supplied to equalizer 208 to equalize the data in each subcarrier. As with conventional OFDM systems, a simple one-tap equalizer can be used.

After being equalized at each subcarrier, data corresponding to a particular user is separated by subcarrier demapping unit 210, which is opposite to the operation performed by subcarrier mapping units 104, 114 at transmitter 100. In the non-spread OFDMA subassembly 240, each user data 211 is simply converted to serial data 217 by the S / P converter 216. In spread OFDMA subassembly 230, data 212 on the separated subcarrier is further processed by code domain user separation unit 214. Depending on how spreading is performed at the transmitter 100, corresponding user separation occurs at the code domain user separation unit 214. For example, if 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 spreading in the transmitter 100 is only in the frequency domain, a conventional (frequency domain) despreader may be used as the code domain user separation unit 214. If spreading is done in both the time domain and the frequency domain at the transmitter 100, then the time-frequency rake combiner can be used as the code domain user separation unit 214.

5 is a block diagram of an exemplary time-frequency rake combiner 500 constructed in accordance with the present invention. The time-frequency rake combiner 500 processes in both time and frequency domains to recover data spread in both the time and frequency domains at the transmitter 100. The time-frequency rake combiner 500 may be implemented in a variety of ways, and the configuration shown in FIG. 5 is provided by way of example and not by way of limitation, and the scope of the present invention is not limited to the structure shown in FIG.

Time-frequency rake combiner 500 includes despreader 502 and rake combiner 504. In the spread OFDMA subassembly 230, data 212 collected separately for a particular user by the subcarrier demapping unit 210 shown in FIG. 1 is transferred to the despreader 502. Despreader 502 performs frequency domain despreading on data 212 on the subcarrier. The despreader 502 includes a plurality of multipliers 506 that multiply the conjugate 508 of the spreading code with the data 212, a summer 512 that sums the product output 510, and a normalization that normalizes the summed output. And a riser 516. Despreader output 518 is then processed by Rake combiner 504 to time-domain combine to recover the user's data.

Referring back to FIG. 1, the transmitter 100, the receiver 200, or both may include a plurality of antennas, and the hybrid OFDMA according to the present invention may be connected to the plurality of antennas at the transmitting side, the receiving side, or both sides. It can be implemented together.

While specific features and elements of the invention have been described in particular embodiments that combine particular features, each feature and element may be used alone, in combination with, or with other features and elements of the invention, other features and elements of the preferred embodiments. It can be used in various combinations without.

100: Transmitter
102: diffuser
104, 114: subcarrier mapping unit
112: S / P converter
122: N-point IDFT processor
124: P / S Converter
126: CP insertion unit
130, 230: spread OFDMA subassembly
140, 240: non-spread OFDMA subassembly
150, 250: common subassembly
200 receiver
210: subcarrier demapping unit
208: Equalizer
206: N-point DFT processor
204: S / P Converter
202: CP removal unit

Claims (18)

In a wireless transmit / receive unit (WTRU) configured to perform orthogonal frequency division multiple access (OFDMA) communication,
A receiver configured to receive OFDMA symbols at a symbol time interval,
The OFDMA symbols are multi-user input data spread using orthogonal sequences on a first group of subcarriers and input data not spread using orthogonal sequences on a second group of subcarriers. Wherein the multi-user input data is for a plurality of users, wherein the multi-user input data is spread using a plurality of orthogonal sequences, each of the plurality of orthogonal sequences associated with an individual user of the plurality of users. Become,
The receiver recovers single-user input data from the first group of subcarriers, wherein the single user input data is recovered by despreading the multi-user input data from the first group of subcarriers. )-Recover and recover the input data from the second group of subcarriers. The method of claim 1,
Wherein the multi-user input data is spread in at least one of a time domain or a frequency domain. The method of claim 1,
And wherein the OFDMA symbol comprising multiple user input data is produced by repeating the single user input data. The method of claim 1,
And the receiver is configured to recover a common pilot transmitted on the first group of subcarriers. The method of claim 1,
And the receiver performs at least one of time-domain hopping or frequency-domain hopping in demapping the input data from the second group of subcarriers. The method of claim 1,
And the receiver comprises a rake combiner. The method of claim 1,
And the receiver comprises a time-frequency rake combiner. The method of claim 1,
And the receiver comprises a plurality of antennas. The method of claim 1,
And the wireless transmit / receive unit is configured as a user equipment (UE). In the method for orthogonal frequency division multiple access (OFDMA) communication in a wireless transmit / receive unit (WTRU),
Receiving OFDMA symbols at a symbol time interval, wherein
The OFDMA symbols are multi-user input data spread using orthogonal sequences on a first group of subcarriers and input data not spread using orthogonal sequences on a second group of subcarriers. Wherein the multi-user input data is for a plurality of users, wherein the multi-user input data is spread using a plurality of orthogonal sequences, each of the plurality of orthogonal sequences associated with an individual user of the plurality of users. The receiving step; And
Single-user input data from the first group of subcarriers, wherein the single user input data is recovered by despreading the multi-user input data from the first group of subcarriers. Recovering and recovering the input data from the second group of subcarriers. 10. The method of claim 1, further comprising recovering the input data from the second group of subcarriers. The method of claim 10,
And wherein the multi-user input data is spread in at least one of a time-domain or a frequency-domain. The method of claim 10,
And the OFDMA symbols comprising multiple user input data are produced by repeating the single user input data. The method of claim 10,
Recovering a common pilot transmitted on the first group of subcarriers. 10. The method of orthogonal frequency division multiple access (OFDMA) communication in a wireless transmit / receive unit. The method of claim 10,
Orthogonal frequency division multiplexing in a wireless transmit / receive unit, wherein at least one of time-domain hopping or frequency-domain hopping is performed in demapping the input data from the second group of subcarriers. Method for access (OFDMA) communication. The method of claim 10,
Separating the single user input data from the first group of subcarriers with a rake combiner. 10. The method for orthogonal frequency division multiple access (OFDMA) communication in a wireless transmit / receive unit. The method of claim 10,
Separating the single user input data from the first group of subcarriers in a code domain using a time-frequency rake combiner for orthogonal frequency division multiple access (OFDMA) communication in a wireless transmit / receive unit. Way. The method of claim 10,
The method is performed by a user equipment (UE), orthogonal frequency division multiple access (OFDMA) communication in a wireless transmit / receive unit. delete

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