KR101144454B1 - Two-step radio resource management method for downlink of multiuser ofdma system with heterogeneous quality of service requirements - Google Patents

Abstract

A radio resource allocation method for downlink in an OFDMA system in a multi-user environment, the method comprising: calculating a transmission power to be allocated to a user using a power cancellation coefficient including a propagation loss of the user and a fading channel; Calculating a required bandwidth required from the user using the threshold values for the transmit power and the SNR, and the power cancellation coefficients; And allocating a bandwidth corresponding to a required bandwidth within a limited bandwidth that is a bandwidth provided by an OFDMA system.

Description

TWO-STEP RADIO RESOURCE MANAGEMENT METHOD FOR DOWNLINK OF MULTIUSER OFDMA SYSTEM WITH HETEROGENEOUS QUALITY OF SERVICE REQUIREMENTS}

Embodiments of the present invention relate to a radio resource allocation algorithm for downlink in a multi-user OFDMA system that meets heterogeneous QoS requirements.

Typically, a wireless communication system is a communication system for ensuring the user's activity free from the distance constraints of the wire. Such a wireless communication system has been actively studied and used a communication system using orthogonal frequency division multiple access (CDMA). However, the CDMA scheme has been actively discussed for the OFDMA scheme that can provide more data due to the problem that it is difficult to provide more data services required by users due to limited resources. Reached.

Orthogonal Frequency Division Multiple Access (OFMDA) is basically a method of transmitting data using a multi-carrier based on an Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing) method. Therefore, orthogonal frequency division multiplexing converts symbol strings that are serially input in parallel so that each of them has a plurality of sub-carriers, that is, a plurality of sub-carrier channels. This is a type of multicarrier modulation that modulates and transmits data. The OFDMA system adopts orthogonal frequency division multiplexing as a basic transmission method and allocates different subcarriers to different users through the plurality of subcarriers.

In the OFDMA system, the application of the relay system combined with the multi-antenna technique can reduce the outage probability and coverage hole in the service area, thereby increasing the overall system yield. However, a new concept of radio resource management algorithm for the radio link relay It is required.

Recently, the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) -Advanced system is an improved system of 3GPP LTE and is currently being standardized by the 3GPP group. In 3GPP LTE-Advanced system, wide bandwidth, spatial multiplexing through increased antenna, and cooperative transmission and reception are required to support high data rates.

In order to apply the radio relay concept to the 3GPP LTE-Advanced system, it is possible to provide an integrated frame structure suitable for cooperative transmission and non-transparent and having low latency.

A new opportunistic subchannel and power allocation algorithm can be provided to maximize the yield of the system in relay systems and multi-antenna environments while meeting heterogeneous QoS requirements.

A method for allocating a radio resource for downlink in an orthogonal frequency division multiple access (OFDMA) system in a multi-user environment, the method comprising: allocating the same transmit power to all users who request data transmission; Calculating the required bandwidth required by each user using a number of users, threshold values for transmit power and signal-to-noise ratio (SNR), and power cancellation coefficients including the user's path-loss and fading channel ; Allocating a bandwidth corresponding to a required bandwidth within a limited bandwidth that is a bandwidth provided by an OFDMA system; And reassigning transmit power using the power cancellation coefficients.

A radio resource allocation method for downlink in an OFDMA system in a multi-user environment, the method comprising: calculating a transmission power to be allocated to a user using a power cancellation coefficient including a propagation loss of the user and a fading channel; Calculating a required bandwidth required from the user using the threshold values for the transmit power and the SNR, and the power cancellation coefficients; And allocating a bandwidth corresponding to a required bandwidth within a limited bandwidth that is a bandwidth provided by an OFDMA system.

According to one side, if the total bandwidth allocated to all users requesting data transmission exceeds the limited bandwidth, it is possible to normalize the allocated bandwidth (normalization).

According to another aspect, the number of subchannels to be allocated to the user may be determined using the bandwidth and the required bandwidth of the subchannel provided by the OFDMA system.

A method for allocating a radio resource for downlink in an OFDMA system in a multi-user environment, comprising: determining a subchannel allocation order using an average data rate for transmitting data through one subchannel by a user requesting data transmission ; And allocating a subchannel of the user according to the subchannel allocation order.

A radio resource allocation method for downlink of an OFDMA system in a multi-user environment, the method comprising: arranging channel state information of a user requesting data transmission; And allocating a subchannel satisfying the target data rate of the user to the user using the channel state information.

According to one side, in a state in which the user has not been allocated the subchannels, the remaining unallocated subchannels are sorted based on the channel state information fed back from the user who has allocated the subchannels, and then the channel state information is in the highest order. Subchannels can be allocated.

Through the integrated frame structure that can be applied to the 3GPP LTE-Advanced system, the wireless relay concept can support cooperative transmission and relay transmission and realize low latency.

By providing a new opportunistic subchannel and power allocation algorithm, the system yield can be maximized in relay systems and multi-antenna environments.

In addition to the existing beamforming and MIMO techniques, new beamforming techniques such as opportunistic beamforming and cooperative collision avoidance beamforming to avoid interference in overlapping regions of multiple cells can be applied to relay systems. Can be.

It provides an optimized and semi-optimal heuristic solution for opportunistic subchannels and power allocation algorithms, and compares / analyzes the complexity of suboptimal opportunistic subchannels and power allocation algorithms for system application.

1 is a flowchart illustrating a radio resource allocation method for a BE service in a wireless OFDMA system according to an embodiment of the present invention.
Figure 2 shows the yield loss rate in a flat Rayleigh fading channel environment using the bandwidth and power allocation algorithm proposed in the present invention.
Figure 3 compares the outage probability of the bandwidth and power allocation algorithm proposed in this embodiment in a flat fading channel environment.
4 shows the relative yield increase rate of the subchannel allocation algorithm proposed in the present invention.
5 is a flowchart illustrating a radio resource allocation method for RT service in a wireless OFDMA system according to an embodiment of the present invention.
6 illustrates a subchannel allocation algorithm in a wireless OFDMA system according to an embodiment of the present invention.
FIG. 7 illustrates a CDF (cumulative distribution function) according to a user data rate of a radio resource allocation method comprising a user priority determination step and a subchannel assignment step.
FIG. 8 illustrates a CDF (cumulative distribution function) according to a user scheduling delay of a radio resource allocation method including a user priority determination step and a subchannel assignment step.
FIG. 9 illustrates a radio resource management process proposed in the present invention to support two hops in a nontransparent RS of a 3GPP LTE-Advanced system.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

An embodiment of the present invention uses a relay technology through a relay station (RS), which has low system installation cost, to increase overall system yield and coverage in a wireless orthogonal frequency division multiple access (OFDMA) system. According to a duplexing method between a link between a base station and a user and a relay link through an RS, relay wireless communication is divided into two types, an inband relay and an outband relay. In the case of in-band relay, the time-division method uses the same time slot but different time slots between the two links. RS is divided into two types, non-transparent RS and transparent RS, both of which are used in 3GPP LTE-Advanced system. Non-transparent RS is mainly used to support coverage extension or coverage area of service area, and transparent RS is used to improve overall system yield.

An embodiment of the present invention provides an integrated relay frame structure consisting of a transparent mode and a non-transparent mode for two-hop / multi-hop support. In addition, it provides a relay-based opportunistic subchannel and power allocation algorithm through the requirements of the 3GPP LTE-Advanced system.

A radio resource allocation method for downlink in a wireless OFDMA system according to an embodiment relates to an opportunistic radio resource management algorithm supporting a best-effort service and a real-time service. The result of the present embodiment can be applied to 3GPP LTE system and 3GPP LTE-Advanced system using the OFDMA communication method in the downlink.

For the BE service, the present embodiment can provide a new subchannel allocation algorithm for simultaneously obtaining fairness and multi-user diversity gain in an OFDMA system.

1 is a flowchart illustrating a radio resource allocation method for a BE service in a wireless OFDMA system according to an embodiment of the present invention.

In step 110, the wireless OFDMA system allocates bandwidth and power for each user. At this time, the algorithm for allocating bandwidth and power can be summarized into three types.

First algorithm

(1) Allocate bandwidth for each user.

(1-1) Allocate the same transmit power to each user to allocate bandwidth.

(1-2) The required bandwidth of the i-th user must satisfy the SNR (signal-to-noise ratio) threshold γ for outage. That is, the required bandwidth of the i-th user may be defined as in Equation 1.

Where N is the number of users trying to transmit data, N ₀ is the AWGN (additional white Gaussian noise) noise power, γ is the SNR threshold for outage, and g _i is the path-loss of the ith user. And a power cancellation coefficient including a fading channel.

(1-3) The actual allocated bandwidth of the i-th user is calculated through Equation 2 using the bandwidth calculated in (1-2).

(2) Allocate a transmission power calculated by Equation 3 to each user. That is, the transmission power to be substantially allocated to the i-th user is calculated.

Second algorithm

(1) The transmission power is allocated to each user according to equation (3).

(2) Allocate bandwidth for each user.

(2-1) The required bandwidth of the i-th user is calculated by equation (4).

(2-2) The actual bandwidth of the i-th user is calculated through Equation 2 using the bandwidth calculated in (2-1).

Third algorithm

(1) The transmission power is allocated to each user according to equation (3).

(2) The bandwidth for each user is allocated by Equation 4. In this case, when the total bandwidth allocated to all users is larger than B, the system bandwidth limit value, bandwidth normalization is performed using Equation 2.

In step 120, the wireless OFDMA system allocates a subchannel to each user when allocating bandwidth and power using one of the three algorithms described above. The number of subchannels to be allocated to each user is calculated through Equation 5.

Here, N _i represents the number of subchannels allocated to the i- th user and B _sub represents the bandwidth of the subchannel.

In the above subchannel allocation algorithm, each user selects the subchannel having the best channel condition with respect to the subchannel N _i allocated to the subchannel, but if multiple users select the same subchannel, priority is determined for subchannel allocation. The method is made by the equation (6).

는 i 사용자가 모든 부채널을 통해 전송할 시의 평균 비트수를 나타낸다.Where n and i are subchannels and user indices, R _{n , i} are the number of bits i user can transmit on n subchannels, and

It is i denotes a user and average number of bits at the time of transfer through all subchannels.

FIG. 2 shows the yield loss rate in a flat Rayleigh fading channel environment using the bandwidth and power allocation algorithm proposed in this embodiment when five users are uniformly distributed in a cell. As shown in FIG. 2, it can be seen that the second and third algorithms have improved performance compared to the first algorithm. When γ (SNR threshold for outage) is larger than 5 dB, the third algorithm is the second algorithm. Better performance than

Figure 3 compares the outage probability of the bandwidth and power allocation algorithm proposed in this embodiment in a flat fading channel environment. To check outage performance over distance, fix the user's position so that d ( i ) = 0.2ikm. Here, d ( i ) means the distance between the i- th user and the BS (base station). In FIG. 3, the outage probability is proportional to the distance of the user through the existing algorithm (best UE bandwidth and power allocation method) and the first algorithm. In the conventional algorithm, the second to fifth users have a high outage probability, which does not guarantee the fairness of the whole system. However, the first algorithm reduces the outage probability of the second to fifth users compared to the existing algorithm, and the outage probability of all users is 0.09% and 0% for the second and third algorithms. Therefore, the bandwidth and power allocation algorithm proposed in this embodiment can guarantee the fairness of the overall system through the balance of outage probabilities by equally giving all users the opportunity to transmit data.

4 shows a relative yield increase rate of the subchannel allocation algorithm proposed in this embodiment. 4 shows the yield increase rate in the ITU-R Veh-A channel environment having a flat fading channel and a moving speed of 30 km / h through the equation (7). When the outage SNR threshold is 0 dB in an ITU-R Veh-A channel environment with a travel speed of 30 km / h, the yield of 37% is increased by using the radio resource allocation method of the present embodiment, but in a flat fading channel environment. Since there is no frequency selectivity of the channel, no increase in yield is seen.

In addition, the present embodiment provides a new radio resource allocation method for guaranteeing the quality of service (QoS) between heterogeneous users for the RT service.

5 is a flowchart illustrating a radio resource allocation method for RT service in a wireless OFDMA system according to an embodiment of the present invention.

The radio resource allocation method according to an embodiment includes a user priority determination step 210 and a subchannel allocation step 220. The scheduling delay and the target data rate are guaranteed through the user prioritization step 210 and the subchannel allocation step 220.

First, in the user prioritization step 210, the subchannel allocation order for each user is determined in consideration of the scheduling delay. Subchannels of each user are allocated according to the determined order.

The user priority is determined as shown in Equation 8.

은 k 번째 사용자가 하나의 부채널을 통해 전송할 수 있는 평균 데이터 전송률이다.here,

Is the average data rate that the kth user can transmit on one subchannel.

Next, in the subchannel allocation step 220, a new subchannel allocation algorithm is proposed to satisfy the target data rate of the user. Here, the subchannel allocation algorithm has four steps.

(1) Channel state information of each user is arranged.

(2) If the m-th user has a good channel condition in the sub-channel q through the channel state information, the sub-channel q is assigned to the m-th user. In addition, when a plurality of users have a good channel condition in the subchannel q, the user who uses the subchannel q is determined through Equation (9).

(3) The above process (2) is repeated until the m th user satisfies the target data rate.

(4) If the subchannel for satisfying the target data rate of the m-th user has not been allocated, the unassigned subchannels are sorted based on the channel state information fed back by the m-th user. Thereafter, the data is allocated to the m th user in order from the subchannel having the high channel state information until the target data rate is satisfied.

The subchannel allocation algorithm composed of the above steps (1) to (4) can be defined as shown in FIG. 6, which can simultaneously obtain a frequency diversity gain and a multi-user gain in an OFDMA system.

FIG. 7 illustrates a CDF (cumulative distribution function) according to a user data transmission rate of a radio resource allocation method comprising a user priority determination step and a subchannel assignment step in this embodiment. 7 shows that the radio resource allocation method of the present embodiment improves CDFs by 28% and 8.5% according to target data rates of user classes 1 and 2, respectively. In addition, it can be seen that the overall performance improvement is proportional to the target data rate of the user.

FIG. 8 illustrates a CDF (cumulative distribution function) according to user scheduling delay in the radio resource allocation method consisting of a user priority determination step and a subchannel assignment step in this embodiment. 8, it can be seen that the radio resource allocation method proposed in this embodiment has a larger delay time due to scheduling than the conventional improved GPF scheduling algorithm. This has a smaller scheduling delay than the algorithm of the present embodiment because the existing algorithm is scheduled in sub-channel order, allowing more users to transmit data at the same time. However, the radio resource allocation method of this embodiment does not cause system performance deterioration because the delay time according to the scheduling satisfies the requirements. Therefore, the radio resource allocation method of the present embodiment can guarantee a higher data rate without causing performance degradation due to increased delay time.

In order to support multi-hop in a 3GPP LTE-Advanced system, a radio resource allocation algorithm according to the above-described embodiment may be applied.

Recently, many researches have been conducted on a communication system that enables high-speed data transmission while reducing costs by using RS in addition to BS. 3GPP LTE-Advanced system is also interested in building a system through such RS. have. The installation of this RS greatly increases the overall yield and coverage of the system. When installing an RS, you need to carefully analyze and install several factors, such as frequency efficiency, installation cost, and optimal RS location. Also, when installing a new RS, there are some problems caused by the existing RS. In the case of Inband RS, time slots for relays must be used to transmit data to multi-hop users, which causes some performance degradation. To solve this problem, cooperative transmission between BS and RS should be considered. In the case of outband RS, an additional transmission frequency for the relay is required, which causes an increase in frequency usage fee, and increases the complexity and cost of hardware for simultaneously transmitting and receiving, and transmitting antenna and Interference problems between receiving antennas also occur.

FIG. 9 illustrates a proposed radio resource management process for supporting two hops in a non-transparent RS of a 3GPP LTE-Advanced system. In the case of the transparent RS, the radio resource allocation method according to an embodiment for the BE service and the RT service can be applied as it is by considering cooperative transmission with an existing installed transparent RS.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

Claims (7)

A radio resource allocation method for downlink in an orthogonal frequency division multiple access (OFDMA) system in a multi-user environment,
Allocating the same transmission power to all users who request data transmission;
Request from each user using the number of users who requested the data transmission, threshold values for the transmit power and signal-to-noise ratio (SNR), and power cancellation coefficients including the user's path-loss and fading channel Calculating a required bandwidth;
Allocating a bandwidth corresponding to the required bandwidth to the user within a limited bandwidth that is a bandwidth provided by the OFDMA system; And
Reallocating the transmit power using the power cancellation factor
Radio resource allocation method comprising a. A radio resource allocation method for downlink of an OFDMA system in a multi-user environment,
Calculating transmission power to be allocated to the user using a power cancellation coefficient including a propagation loss of the user and a fading channel;
Calculating a required bandwidth required from the user using the threshold values for the transmit power and the SNR, and the power cancellation coefficient; And
Allocating a bandwidth corresponding to the required bandwidth to the user within a limited bandwidth, the bandwidth provided by the OFDMA system;
Radio resource allocation method comprising a. The method of claim 2,
Performing normalization on the allocated bandwidth if the total bandwidth allocated to all users who request data transmission exceeds the limit bandwidth.
Radio resource allocation method further comprising. The method according to claim 1 or 2,
Determining a number of subchannels to be allocated to the user using a bandwidth of a subchannel provided by the OFDMA system and the requested bandwidth.
Radio resource allocation method further comprising. delete delete delete

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