Zhang Ping

Sub-Carrier Coupling for OFDM based AF Multi-Relay Systems

Amplify and forward (AF) is an effective mode for relaying systems with ease for implementation. In a conventional orthogonal frequency division multiplexing (OFDM) based AF system, relay stations simply amplifies the received signals and forward them to the destination station. Due to the fact that channel transfer function for the first hop (sourcerelay) and the second hop (relay-destination) may vary a lot, system capacity is limited. This contribution introduces a method named sub-carrier coupling, which couples subcarriers for the two hops in a certain rule to improve system capacity. Firstly, system with a single relay station and its capacity is discussed, and the coupling scheme to maximize the system capacity is proposed. Then system with multiple relay stations is investigated, and two solutions are proposed. The solution with sub-carrier coupling can bring to much higher capacity since it determines the sub-carrier coupling scheme and assigns relay stations to forward signal for all sub-carriers jointly. Numerical simulation is carried out to show the efficiency of the proposed solutions.

New detection algorithm of V-BLAST space-time code

Space-time code techniques have been widely studied in wireless communications, for they provide better signal qualities in fading channel environments and increase the system capacity. As an important space-time code, Bell Lab Layered Space-Time (BLAST) code has been paid more attention. However, the traditional detection algorithm of V-BLAST space-time code needs much time to perform linear combination nulling and successive symbol cancellation. The greater the number of transmit antennas, the greater the time delay. To overcome this disadvantage, a new scheme based on linear combination nulling and parallel symbol cancellation is proposed. The new scheme has a lower time delay. The simulation results of this new scheme are obtained by COSSAP simulation in flat Rayleigh channels. These simulation results are presented to verify the BER performance of the new scheme based on parallel symbol cancellation.

Closed loop space-time block code

In 3GPP FDD specifications, space time transmit diversity (STTD) employs space-time block code (STBC) to maintain orthogonality between the two antennas in order to avoid self-interference in fading channels. However, the STTD technique is just open loop transmit diversity, and we investigate whether we can obtain further gain if closed loop STBC is used. A novel scheme based on closed loop STBC is proposed first. And then an optimized allocation scheme of a fixed transmitter power budget between two transmit antennas is presented. Finally, COSSAP simulation results show a significant performance improvement between closed loop STBC and traditional STBC. Moreover, these simulation results also show a good agreement with our theoretical analyses.

Performance of LDPC Coded AOFDM Under Frequency-Selective Fading Channel

In this paper, LDPC code is combined with adaptive OFDM. Code rate of LDPC is fixed and modulation mode of sub-carriers can vary according to CQI. Throughput analysis of the scheme under frequency-selective fading channel and theory of sub-band based LDPC coded AOFDM is given. Computer simulation under 12-tap TU fading channel was carried out. Results show that the LDPC coded AOFDM scheme exhibits BER performance quite close to that with fixed QPSK modulation due to existence of LDPC, meanwhile brings much higher throughput than non-adaptive schemes because of adaptation. The sub-band based adaptation has a little degradation in throughput, but reduces signaling cost greatly. LDPC coded AOFDM guarantees system reliability and improves throughput a lot

Call routing and admission control for two-hop TDMA cellular system

In future wireless communication systems, an architecture introducing wireless relaying technologies into the cellular infrastructure, seems a promising approach to enlarge the coverage area and enhance system capacity. How to design an efficient call admission control algorithm to perform routing and channel allocation for such integrated cellular system, and manage the radio resources effectively are the key issues to be studied. Based on time division multiple access (TDMA) scheme, this paper proposes a novel call routing and admission control (CRAC) algorithm for the two-hop cellular system with the aim of extending system coverage and increasing system capacity cost-effectively. With the proposed CRAC algorithm, a mobile terminal (MT) can choose the conventional direct link or opt for the relaying considering the transmission quality as well as the traffic load balance. The simulation results show that the CRAC algorithm can decrease the blocking probability significantly and increase the system capacity and enhance the coverage by utilizing the limited channel resource efficiently. Keywords-Relaying, Call routing and admission control (CRAC), Cellular

Adaptive Bit, Power Allocation and Sub-Carrier Coupling for AF-OFDM Relaying Systems

Link adaptation technique is applied in an amplify and forward (AF) - orthogonal frequency division multiplexing (OFDM) relaying system, and adaptive bit and power allocation (ABPA) is investigated for such system. ABPA problem is presented first, and the optimal solution is proposed with aid of Greedy algorithm. Because channel transfer functions for two hops are independent, which limits throughput of a conventional AF-OFDM system, we take sub-carrier coupling (SQ into account. Two solutions are proposed for the problem with ABPA and SC; the first adopts a concatenated method to realize SC and ABPA with two steps, and the second utilized a joint way to adjust SC and allocated bits and power. Numeral simulation results show that the proposed ABPA solution can improve throughput greatly while guaranteeing bit error rate (BER) requirement very well. When SC is involved, more improvement can be obtained; the joint solution outperforms the concatenated solution.

Multistage non-linear parallel interference cancellation with small spread factor

Aiming at the question of interference regeneration with small spread factors for frequency selective Rayleigh fading CDMA systems, we propose a concept of attenuation factors and a novel scheme of multistage nonlinear parallel interference cancellation (PIC) based on attenuation factors. Moreover, we analyze the effects of the attenuation factors of multistage non-linear PIC with small spread factors. Computation results show to what extent the performance can be improved.

Suppress multi-access interference detector based on software radio architecture

A novel receiver architecture of multi-user detection for direct-sequence spread-spectrum multiple-access communication systems is considered. We outline a configurable architecture via software radio implementation of this receiver. In order to reduce the computational configuration, we partition functionality into two core.

LDPC Coded AMC Based on Decoding Iteration Times for OFDM Systems

A low-density parity-check (LDPC) coded adaptive modulation and coding (AMC) strategy is presented for orthogonal frequency division multiplexing (OFDM) systems. Since system performance is improved as the maximum iteration times for LDPC decoding increase, iteration times for decoding reflect channel quality. We first propose an AMC strategy to utilize the information of iteration times for decoding to adopt higher order modulation and coding schemes (MCS) than the conventional strategy, so as to improve system throughput. Since it may bring worse reliability, hybrid automatic repeat request (H-ARQ) is used in a second strategy. Simulation under typical urban channel is carried out, and the results show the proposed strategies can bring higher throughput, and the strategy with H- ARQ can improve throughput and guarantee reliable transmission simultaneously.

Group Cell Architecture for Future Mobile Communication System

This paper describes some new contributions to the Generalized Distributed Antenna Architecture-Group Cell for future mobile communication system. The system architecture is described which allows the integration of multiple antenna techniques, e.g., MIMO, by spaced MIMO, distributed MIMO and virtual MIMO structure. The Slide Handover strategy based on the Group Cell architecture is also introduced with the Minimum Dwelling Time (MDT) based channel reserved prioritization algorithm in details. The capacity of Group Cell architecture and the performance of MDT algorithm based Slide Handover are analyzed. System level simulation results are given to show the performance increment of Group Cell architecture and Slide Handover strategy respectively.