In this paper, the benefit of linear precoding along with distributed orthogonal space time block codes (OSTBCs) is exploited to improve the performance of distributed antenna system (DAS). In particular, we propose a novel precoder design method based on channel angular domain parameters, i.e., average angle of arrival (AOA), angular spread (AS), normalized antenna spacing (NAS) and Ricean K-factor, instead of the conventional channel correlation matrix which has been widely used to characterize MIMO channel. Built on the distributed characteristics of DAS, a more realistic non-Kronecker channel model is established, and then the optimal precoder is designed as a function of the above angular domain parameters. Asymptotic analysis reveals that, the optimal precoder acts as a combination of channel precoder and power allocator. Furthermore, the impact of the above angular domain parameters on system performance, including diversity order and coding advantage, is investigated in detail. Specifically, we find that better gain can be achieved with larger K-factor. Finally, our theoretical claims are confirmed by the numerical results.

Exploiting Channel Angular Domain Information for Precoder Design in Distributed Antenna Systems

This paper presents a novel unequal error protection (UEP) video transmission scheme based on dynamic resource allocation in a MIMO-OFDM system in order to improve the video transmission performance over wideband wireless channels. In this new scheme, a low density parity code (LDPC) is combined with a complexity reduced power reallocation algorithm to utilize the excess powers which margin from the powers necessary to meet the modulation level selected under a certain BER constraint. Furthermore, by taking full advantage of the residual excess powers, unequal error protection on important bits of video streams is provided by the LDPC code. Accordingly, the transmission efficiency and quality are both increased. Simulation results have shown that the proposed scheme may achieve great improvement in both systems with or without perfect channel estimation.

UEP Video Transmission Based on Dynamic Resource Allocation in MIMO OFDM System

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space---time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

In wireless broadband communications, orthogonal frequency division multiplexing (OFDM) has been adopted as a promising technique to mitigate multi-path fading and provide high spectral efficiency. In addition, cooperative communication can explore spatial diversity where several users or nodes share their resources and cooperate through distributed transmission. The concatenation of the OFDM technique with relaying systems can enhance the overall performance in terms of spectral efficiency and improve robustness against the detrimental effects of fading. 

Hybrid relay selection is proposed to overcome the drawbacks of conventional forwarding schemes. However, exciting hybrid relay protocols may suffer some limitations when used for transmission over frequency-selective channels. The combination of cooperative protocols with OFDM systems has been extensively utilized in current wireless networks, and have become a promising solution for future high data rate broadband communication systems including 3D video transmission. This thesis covers two areas of high data rate networks. In the first part, several techniques using cooperative OFDM systems are presented including relay selection, space time block codes, resource allocation and adaptive bit and power allocation to introduce diversity.

Four (4) selective OFDM relaying schemes are studied over wireless networks; selective OFDM; selective OFDMA; selective block OFDM and selective unequal block OFDM. The closed-form expression of these schemes is derived. By exploiting the broadcast nature, it is demonstrated that spatial diversity can be improved. The upper bound of outage probability for the protocols is derived. 

A new strategy for hybrid relay selection is proposed to improve the system performance by removing the sub-carriers that experience deep fading. The per subcarrier basis selection is considered with respect to the predefined threshold signal-to-noise ratio. The closed-form expressions of the proposed protocol in terms of bit error probability and outage probability are derived and compared with conventional hybrid relay selection. Adaptive bit and power allocation is also discussed to improve the system performance. 

Distributed space frequency coding applied to hybrid relay selection to obtain full spatial and full data rate transmission is explored. Two strategies, single cluster and multiple clusters, are considered for the Alamouti code at the destination by using a hybrid relay protocol. The power allocation with and without sub-carrier pairing is also investigated to mitigate the effect of multipath error propagation in frequency-selective channels.

The second part of this thesis investigates the application of cooperative OFDM systems to high data rate transmission. Recently, there has been growing attention paid to 3D video transmission over broadband wireless channels. Two strategies for relay selection hybrid relay selection and first best second best are proposed to implement unequal error protection in the physical layer over error prone channels. The closed-form expressions of bit error probability and outage probability for both strategies are examined. The peak signal-to-noise ratio is presented to show the quality of reconstruction of the left and right views.

Adaptive relaying protocol multiple-input multiple-output orthogonal frequency division multiplexing systems

In current 4G system given in recent literatures, channel estimation overhead and complexity of multi-user detectors (MUD), may lead to bad performance in fast fading channel scenarios when large number of users exists. So, a novel 4G system with TDD/TDMA as duplex and wireless access is designed to reduce channel estimation spending and avoid MUD, as only one user can be active to communicate with base station. Under the requirement of 4G systems, radio frame structure is elaborately designed to fit for fast fading channel scenarios. Construction of training sequences for channel estimation is also detailed together with a novel eigenmodes coupled universal space-time codes. The system architecture with consideration of link adaptations is given and evaluated for performance of TDD/TDMA 4G systems. Results show the proposed TDD/TDMA 4G can meet the requirement of 4G system under the classical ITU channel profiles.

/pdf/limitations-of-current-4g-systems-and-its-substitute-schemes-4bc0gohomi.pdf

Limitations of current 4G systems and its substitute schemes with TDD/TDMA

In this paper, the combination of orthogonal frequency-division multiplexed (OFDM), multi-input multi-output (MIMO) and adaptive modulation can effectively eliminate or resist various fading in wireless channels, thus it can improve the capacity of system and transmission quality. Depending on the optimal bit and power allocation strategy based on greedy algorithm, in this paper, the performance of adaptive bit and power allocation MIMO-OFDM system based on greedy algorithm is completely studied. And the performance comparison among greedy algorithm, Chow algorithm and average algorithm is represented. We also compare the performance of MIMO-OFDM system under different antennas numbers. It is shown that the bit error rate (BER) of MIMO-OFDM system based on greedy algorithm is better than that based on Chow algorithm and average algorithm. And the spectral efficiency of greedy algorithm is superior to that of Chow and average algorithm. Ultimately, we show that the performance of MIMO-OFDM system is also superior to that of OFDM system with single transmit antenna and receive antenna which is under the same scheme as the former.

Performance of adaptive bit and power allocation MIMO-OFDM system based on greedy algorithm

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Performance of adaptive bit and power allocation MIMO-OFDM system based on greedy algorithm