In order to improve the V-BLAST/OFDM systems’ performance, we study the subcarrier allocation arithmetic with different detection mode and the obtained multi-user diversity gain. Using the theory of the order statistics and random matrices, we analyse the system’s performance and got the multi-user diversity gain’s math expression. Simulation results indicate that the proposed subcarrier allocation arithmetic can exploit multi-user diversity effectively and improve the V-BLAST/OFDM systems’ performance prominently. Moreover, compared to the spatial diversity systems, simulation results also demonstrate that subcarrier allocation with V-BLAST/OFDM can improve the system performance further.

This paper studies the reverse link power saving characteristic of relay enhanced cellular network, in which the relays are placed at fixed locations and each wireless route includes at most one relay. Results of theoretical analysis and intensive computer simulation have proved that, under the same demand of wireless link qualities as the conventional cellular network, the necessary transmission powers of mobile terminals can be significantly saved even if the relays share the radio resources of the conventional network.

In this paper, the subcarrier allocation problems for downlink transmission of spatial multiplexing based OFDM systems are investigated. With the goal of maximizing the instantaneous capacity, two categories of subcarrier assignment criteria are derived, that is, exclusive manner based criteria which allocate each subcarrier to a single user, and shared manner based criteria which allow multiple users to share a subcarrier. Simulation results demonstrate that both the presented criteria are capable of utilizing the multiuser diversity to enhance the capacity of spatial multiplexing based OFDM systems significantly. Furthermore, via experiments we find that compared with shared criteria, allocating each subcarrier to a single user is a feasible choice to achieve tradeoff among complexity, overhead, and capacity enhancement

In this paper, we propose a dynamic subcarrier and power allocation. algorithm for MIMO/OFDM multiuser communication systems with beamforming in downlink transmission. The algorithm adaptively controls multiple-access, transmit power and beamforming to exploit the channel variation in space, frequency and user domains. The ultimate objective of the loading algorithm is to optimize the overall power efficiency while ensuring the fulfillment of every user's QoS requirements. Numerical results show that significant improvement in performance is achievable with reasonable complexity when the above schemes are applied.

In this paper, the impact of multiuser diversity for V-BLAST based OFDM systems in frequency selective fading channel is considered, and a multiuser subcarrier allocation criterion is developed aimed to optimizing the system-level performance. Mathematical analyses and numeric simulations demonstrate that the proposed subcarrier assignment strategy outperforms the static assignment scheme significantly, even with little amount of feedback. In order to guarantee the users' quality of service (QoS), a reallocation algorithm is given, and it behaves well in our experiments.

Dynamic subcarrier allocation strategies for multiuser OFDM systems in the scenario of SISO are well documented. However, for spatial multiplexing systems, the research on improving the performance by assigning subcarriers dynamically among users seems scarce. In this paper, the impact of multiuser diversity for downlink V-BLAST based OFDM systems is considered, and a multiuser subcarrier allocation criterion is developed for optimizing the system-level performance. For practical implementation, two modified criteria are presented to reduce the complexity and guarantee the fairness among users. Mathematical analyses and numeric simulations demonstrate that the proposed subcarrier assignment strategies outperform the static assignment scheme significantly, even with little amount of feedback. Keywords—MIMO, OFDM, V-BLAST, multiuser diversity, eigenvalue, adaptive subcarrier allocation

This paper investigates the problem of adaptive resource allocation in the downlink of multiuser OFDM systems with V/spl I.bar/BLAST architecture. In order to get a high spectral efficiency even in low SNR, we propose a novel low-complexity adaptive subchannel-bit allocation and power reallocation algorithm. The algorithm considers the users' quality of service (QoS) requirements. Simulation results show that the proposed algorithm performs almost as well as the optimal solution. Moreover, higher spectral efficiency is achieved for larger number of users due to the multiuser diversity and the power reallocation is used in low SNR field.

In wireless networks,bandwidth is extremely valuable resource. Therefore,an effective call admission con- trol is urgent for bandwidth allocation with the occurrence of handoff increasing. The traditional guard channel scheme (GC) and its numerous variants cannot adapt to changes in traffic pattern due to their static nature. Recently, the dynamic method using stochastic control is found to be preferred. But the dynamic control for multi-services is stil1 a problem. The main challenges with multiple types of traffic are that each has its own requirements' bandwidth, QoS guarantee,traffic characteristics and handoff rate. Moreover,the computational complexity is another challenge. In[3],we have set up a novel fictitious stochastic model to get dynamic call admission control. But this model has not considered the complex boundary conditions,so the control precision is not satisfied. In this paper, we consider the boundary conditions and its computation complexity for precision and real time control. As a result,we get an effec- tive multi-services dynamic call admission scheme to adapt for multiple types of sercvies in broadband wireless net- works. Numerical results of simulation show that our scheme steadily satisfies the hard constraint on call dropping probability of multi-services while maintaining a high channel throughput.

As the increasing demand of the capacity of cellular networks, the cell sizes have become smaller than ever, which increases the probability of handoff one may experience during a service. To ensure the calls' QoS and high channel utilization, an effective call admission control is needed urgently. The well-known Guard channel method (GCM) which works with static fashion cannot adapt to the changes in traffic pattern, whereas, SDCA mechanism proposed by S. Wu can overcome that shortcoming due to its dynamic nature. Unfortunately, it is only suitable for single-service. In this paper, we establish a novel stochastic model to study the actual system so as to avoid coping with the complex multiple dimensions stochastic problem. Two wonderful features of the model make it competent for this role. On one hand, it can turn the multiple steps of state transition into single step of state transition, which is a necessary condition for ideal birth-death processes. On the other hand, it can provide a simple method to compute the approximation of the call dropping probabilities for multiple services, which facilitate our estimation for the acceptance ratio vector subject to QoS requirement. As a result, we get a multi-services dynamic call admission scheme to adapt for multiple types of services in mobile wireless networks. Numerical results show that our scheme steadily satisfies the constraint on call dropping probability of multi-services while maintaining a high channel throughput.

There are now great interests in antenna selection strategy for spatial multiplexing systems for the reason that it can reduce cost and complexity yet retain a large part of benefits of multiple antennas. In this paper, we focus on the transmit antenna selection criterion which is applicable to V-BLAST systems with OSIC detection. Based on sub-optimal sorting and QR decomposition, an approximate performance analysis of each sub-stream for V-BLAST transmission is done, and a new solution to the transmit antenna selection problems is suggested. Unlike most of the existing works, this criterion takes into account the impacts of ordering and cancellation. Simulation results show that the proposed algorithm behaves well both in outage capacity and in BER performance. Furthermore, due to the nature of QR decomposition, the implemental complexity can be reduced further by utilizing Gram-Schmidt Orthogonalization.

利用基扩展模型,针对平坦快衰落信道提出了差分空时调制方法.它不仅可避免这类信道中难于实现的信道估计,而且可同时获得由多发射天线提供的满空间分集以及由快衰落信道提供的最大Doppler分集.仿真结果验证了设计的优越性.

In this paper, subcarrier and power allocation problems for multiuser multi-antenna OFDM systems are investigated. With the goal of minimizing the total transmit power required and guaranteeing each user's QoS requirements, a low complexity dynamic resource allocation scheme is proposed. It involves adaptive subcarrier assignment, adaptive power control and beamforming. Mathematical analyses and numerical simulations show that the presented algorithm can exploit multiuser diversity to offer significant system-level performance improvement and guarantee different users' QoS requirements effectively.

In this paper, resource allocation problems for multiuser space-time block coding based OFDM systems are investigated. Specifically, with the goal of minimizing overall transmit power, a subcarrier, power assignment criterion and an recursive allocation algorithm which fulfills users' QoS requirements, including bit error rate and data rate constraint are proposed. Analyses and numeric simulations demonstrate that the proposed subcarrier assignment schemes can exploit multiuser diversity to provide significant system-level performance improvement and guarantee different users' QoS requirements effectively.

Subcarrier and bit allocation schemes for SISO-OFDM systems in multiuser downlink scenario are well-documented. In this paper, we extend it to MIMO-OFDM systems and design a transmit scheme as a concatenation of dynamic subcarrier assignment, adaptive modulation and beamforming. With the goal of minimizing the overall transmit power required to meet the target BER, we develop an adaptive OFDM subcarrier allocation approach based on perfect and partial channel information. Simulation results show that our proposed algorithm outperforms the multiuser MIMO-OFDM with static FDMA technique considerably, and can lessen the performance loss caused by feedback delays. We have also evaluated the performance of the presented system under various number of transmit- and receive-antennas.

Subcarrier and bit allocation schemes for SISO-OFDM systems in multiuser downlink scenario are well-documented. In this paper, we extend it to MIMO-OFDM systems and design a transmit scheme as a concatenation of dynamic subcarrier assignment, adaptive modulation and beamforming. With the goal of minimizing the overall transmit power required to meet the target BER, we propose an adaptive OFDM subcarrier allocation approach based on the maximum eigenvalue (referred to as lambda(max)) of the matrix H (H) H for each user's channel frequency response matrix H, that is, each OFDM subcarrier is assigned to a specific user who has the largest lambda(max) among all users. Simulation results show that our proposed algorithm outperforms the multiuser MIMO-OFDM with static FDMA technique considerably. We have also evaluated the performance of the presented system under various number of transmit- and receive-antennas.

In this paper, channel estimation schemes using pilot signals in the context of MIMO-OFDM systems are investigated. The proposed optimal training sequences can be inserted into every transmitter antenna pilot module synchronously, without vacancy, based on the MMSE principle. We can get more information about the mobile wireless channel, and the optimal pilot sequences derived in this paper outperform both the random and the existing orthogonal pilot sequences that appear to be suboptimal. Furthermore, the proposed method can work even when some transmitters or receivers are disabled, but the existing methods can not.