CN102143588A

CN102143588A - Resource-allocating method for multi-user multi-relay communication system

Info

Publication number: CN102143588A
Application number: CN2011100618570A
Authority: CN
Inventors: 杨绿溪; 吴杨生; 余辉; 李春国
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2011-03-15
Filing date: 2011-03-15
Publication date: 2011-08-03

Abstract

The invention relates to the field of wireless communication and discloses a resource-allocating method for a multi-user multi-relay communication system. The resource-allocating method provided by the invention comprises the following steps of: providing a time division duplex downlink multi-user multi-relay system and allowing a base station sending end (base station) to serve multiple mobile user receiving ends (user) through relays. The system comprises K mobile user receiving ends and R relays. The band width of the system is B and a frequency-selective wideband channel is divided into N flat-fading channels by an orthogonal frequency division multiplexing (OFDM) technology. The base station sending end can serve K mobile user receiving ends through N orthogonal subchannels. Compared with the prior art, the invention has the advantages of higher frequency spectrum efficiency and no extra feedback expenditure. Both K and R are natural numbers and B is a positive rational number.

Description

Resource allocation method of multi-user multi-relay communication system

Technical Field

The invention relates to the field of wireless communication, in particular to a resource allocation method of a multi-user multi-relay communication system.

Background

Research shows that the wireless communication network structure based on the relay station can effectively reduce the waste of power resources caused by path loss, improve the utilization rate of frequency spectrum, and improve the survivability of the network by utilizing the multi-hop communication idea of the ad hoc network, so that the network structure based on the relay station and the cooperative multi-path technology are widely researched and paid attention, and the problem of how to introduce relay cooperative processing is considered when the standards of a new generation of mobile communication, a wireless local area network, a broadband wireless network and the like are established.

The relay enhanced cellular system improves the user communication quality of cell edge areas and hot spot areas by means of relay auxiliary communication, enlarges the cell coverage area, increases the utilization rate of system frequency spectrum resources and improves the overall performance of the cellular communication system. However, due to the increase of relay stations, the traditional cell multi-user scheduling and resource allocation algorithm is no longer applicable, and the design of a novel algorithm becomes a key problem for the research of the relay enhanced cellular system.

A key issue in multi-user communications is how to efficiently handle interference between users, i.e., how to efficiently transmit data for each user. Orthogonal Frequency Division Multiple Access (OFDMA) is a standard technique for solving multi-user multiplexing in a next-generation mobile communication system, and combines OFDM modulation, where OFDMA distinguishes user data over frequency bands, divides a wideband channel into multiple flat fading sub-channels, and theoretically there is no interference between users on different sub-channels, so that data can be efficiently transmitted and received.

The multi-user communication technology using the OFDMA technology is mature, the OFDMA technology is considered when the existing long-term evolution LTE-Advanced proposal relates to the existence of multiple users, the scheme for returning the multi-user communication to the single-user communication needs more bandwidth, the design problem is mainly focused on the subcarrier allocation of an upper layer and the power allocation of a physical layer, and the self-adaptive power resource allocation plays an important role in a cooperative network.

The invention considers the multi-user multi-relay communication system, jointly considers the problems of subcarrier allocation, subcarrier pairing, power allocation and the like, and has obvious gain compared with the existing resource allocation algorithm.

Disclosure of Invention

The technical problem is as follows:the invention aims to provide a resource allocation method of a multi-user multi-relay communication system, so that the multi-user multi-relay communication system obtains satisfactory wireless communication performance.

The technical scheme is as follows:the resource allocation method in the multi-user multi-relay system comprises the following steps:

a. the multi-user multi-relay communication system comprises a base station sending end,

A relay station and

a mobile user receiving end, the mobile users are all two-hop users, wherein

Andare all natural numbers;

b. base station transmit end passA relay station service

The mobile user receiving end acquires the downlink channel information CSI of the two-hop link and distributes the sub-carriers of the second-hop link to the sub-carriers of the second-hop link by utilizing the existing sub-carrier distribution algorithm

A mobile user receiving end;

c. the base station sending end distributes the sub-carrier of the first hop link to the sub-carrier of the second hop link by using the sub-carrier matching technology according to the sub-carrier distribution condition of the second hop link and the channel state information of the first hop link

A plurality of relay stations;

d. under the constraint of total power, a base station sending end distributes transmitting power for subcarriers of a two-hop link according to subcarrier distribution conditions and channel state information of the two-hop link;

e. in the first time slot, a base station sending end sends information of a mobile user to a corresponding relay station according to pre-allocated subcarriers and transmitting power;

f. in the second time slot, each relay station receives the signal sent by the sending end of the base station and decodes and forwards the signal of the mobile user according to the subcarrier distribution condition of the second hop link;

g. and the mobile user receives the signal forwarded by the relay station, decodes the signal and performs corresponding processing.

The relay station is a decoding forwarding relay station; and the two-hop link of the two-hop user adopts the OFDM technology.

The subcarrier allocation algorithm is an algorithm targeted at maximizing system capacity.

The subcarrier pairing technology is that subcarrier channel gains of two-hop links are respectively arranged in a descending order and then paired one by one.

The allocated transmission power is: performing power allocation for the paired sub-carrier pairs allocated to each user by using a water filling algorithm, wherein the power allocation of the sub-carrier pairs is as follows

Wherein

The ratio of the equivalent channel gain of the nth subcarrier pair to the noise at the receiving end is defined as:

wherein

The value of (a) needs to satisfy a total power constraint condition;P _Tis the total transmit power.

And respectively distributing the sending power for the sub-carriers on the two-hop link according to the two-hop channel condition, wherein the expression is as follows:

wherein

Is the transmit power of the base station transmitter on subcarrier m,

the transmit power of relay station r on subcarrier n,

for allocation to the kth user sub-carrier pair

The total power of the power converter,

the signal-to-noise ratio on subchannel n for relay r to the k-th user,

the signal-to-noise ratio on the subchannel m from the sending end of the base station to the relay station r.

Has the advantages that:the Channel State Information (CSI) on each subcarrier of the two-hop link can be obtained by direct channel estimation (TDD system). Compared with the prior art, the invention has higher spectral efficiency and does not increase additional feedback overhead.

Drawings

Figure 1 is a multi-user multi-relay communication system model,

figure 2 is a plot of spectral efficiency versus signal-to-noise ratio for a multi-user multi-relay communication system,

fig. 3 is the Cumulative Distribution Function (CDF) of the spectral efficiency of the system when the signal-to-noise ratio SNR =20 dB.

Detailed Description

According to the inventionThe embodiment discloses a resource allocation method of a multi-user multi-relay communication system, which comprises the following steps: a multi-user multi-relay downlink communication system considering a time division duplex, a base station transmitting end and a relay station

The mobile user receiving end carries out communication. Suppose the system has

At the receiving end of each mobile user,

a relay station, wherein

And

are all natural numbers. System bandwidth of

Will be divided into

A plurality of OFDM sub-carriers, wherein

In order to be a rational number,

is a natural number. The base station transmitting end (base station) needs to pass through

One orthogonal sub-channel transmission

A data stream to

And a mobile user receiving end. Each time, one subcarrier is scheduled to be allocated to only one mobile user receiving end (second time slot) and one relay station (first time slot), and data received by the relay station from one subcarrier can be decoded and forwarded by only one subcarrier of the relay station. It is assumed that the total transmit power of the system is constant.

Representing a set of mobile user receiving ends,

a set of relay stations is represented as,

representing a set of orthogonal subchannels. For each slowly fading subchannel, channel estimation is feasible, where it can be assumed that the base station transmitting end knows all channel information and the system is set to be half-duplex, so that two time slots are needed for communication between the base station transmitting end and the mobile user receiving end.

Suppose that the base station transmitting end transmits data to the relay station r through the subcarrier m, the relay station r then decodes and forwards the data to the mobile user receiving end k through the subcarrier n,,

,

are pairs of subcarriers assigned to the mobile user receiver k.

Is the transmit power of the base station transmitter on subcarrier m,

relay station r in subcarrier nThe transmit power of. Allocated to subcarrier pairs

Total power of

. The single-side power spectral density of the additive white Gaussian noise of the relay station and the mobile user receiving end is assumed to be，

And

respectively representing the channel gain of the first hop channel on the subcarrier m and the channel gain of the second hop channel on the subcarrier n. The definition given for the signal-to-noise ratio is then:

，

. The instantaneous capacity of these two slots can be derived:

and

the base station transmitting end passes through the subchannel pair

To mobile user receiver kThe amount can be expressed as:

in the following, resource allocation is performed with the goal of maximizing system capacity, and in this case, the problem may be defined as:

wherein

Refers to the set of subcarrier pairs assigned to the mobile user receiver k,

is the total system transmit power.

Under the constraint of total power, to make

At the maximum, inevitably have

. Thus is provided with

Then

The maximum value of (d) can be expressed as:

the problem can then be redefined as:

aiming at the problems, the invention provides the following specific implementation steps:

1. the multi-user multi-relay communication system comprises a base station sending end,

A relay station and

a mobile user receiving end, the mobile users are all two-hop users, wherein

And

are all natural numbers;

2. channel State Information (CSI) on each subcarrier of the two-hop link can be obtained through direct channel estimation (TDD system);

3. according to the obtained channel gain of each sub-channel of the second hop link, allocating each sub-carrier of the second time slot to the receiving end of the mobile user with the best channel gain on the sub-carrier,

4. and carrying out subcarrier pairing under the condition that the subcarriers of the second time slot are already allocated. The subcarriers of the two-hop link are sorted by a comparative sorting method and then are paired one by one,

5. after subcarrier allocation and subcarrier pairing, power allocation is performed on the subcarrier pairs, as follows:

wherein,

is the ratio of the equivalent channel gain of the nth subcarrier pair to the receiver-side noise,is the total system transmit power, the solution of the above equation

. After the power of each subcarrier pair is obtained, the power is calculated according to the formula

And formula

Power allocation is performed for the sub-carriers on the two-hop link,

6. the sending end of the base station firstly sends the resource information to the base station according to the pre-allocated resource information

The receiving end of each mobile user transmits data, and the receiving end of each mobile user receives the data on the sub-channels distributed for the receiving end of each mobile user through decoding and forwarding of the relay station.

FIG. 2 is a graph comparing the spectral efficiency of the algorithm of the present invention with that of the prior art (G, Liu, H, Liu, on the capacity of the wideband networks [ C ]. in Proc. IEEE ACSSC' 2004, Pacific Grove, USA, 2004:1318 and 1322) under different SNR, and FIG. 3 is a cumulative probability distribution curve of the spectral efficiency of the two algorithms, which shows that the performance of the algorithm of the present invention is far superior to that of the prior art.