Low Complexity ML Based Interference Cancellation for Layered Space-Time Codes

Orthogonal space-time block codes (STBC), and the Alamouti scheme in particular, are of particular interest in multiple-input multiple-output (MIMO) systems since they achieve full spatial diversity over fading channels and are decoded from linear processing at the receiver. Nevertheless, due to the expensive spectral resource, increasing network capacity requires the development of interference cancellation (IC) techniques allowing several users to share the same spectral resources without impacting the transmission quality. In this context several IC schemes have been developed during this last decade, where each user is equipped with multiple antennas and employs STBC at transmission. However, these IC techniques require multiple antennas at reception, which remains a challenge at the handset level due to cost and size limitations. For this reason, low complexity single antenna interference cancellation (SAIC) techniques, currently operational in GSM handsets, have been developed recently for single antenna users using real-valued modulations or complex filtering of real-valued modulations, by using a widely linear (WL) filtering at reception. Extension to multiple antennas at reception is called multiple antenna interference cancellation (MAIC) technique. The purpose of this paper is to extend the SAIC/MAIC technology to users using both real-valued constellations, such as amplitude shift keying (ASK) constellations, and the Alamouti scheme at transmission. A WL minimum mean square error (MMSE) receiver, completely new for IC purposes in the context of radio communications systems using the Alamouti scheme, is proposed and analyzed. This receiver, which corresponds to the maximum likelihood (ML) receiver for synchronous intranetwork interferences, is able to separate up to 2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> Alamouti users from <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> antennas at reception, hence SAIC capability for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 1.

According to distribute of resource of macro cell and reduce distance between transmitter and receiver, Femto cell system is promising to provide costeffective strategy for high data traffic and high spectral efficient services in future wireless cellular system environment. However, the co-channel operation with existing Macro networks occurs some severe interference between Macro and Femto cells. Hence, the interference cancellation or management schemes are imperative between Macro and Femto cells in order to avoid the decrease of total cell throughput. First, we briefly investigate the conventional resource allocation and interference cancellation scheme between Macro and Femto cells. So we found that cell throughput and frequency reuse ware decreased Then, we propose an adaptive resource allocation scheme based on the distribution of Femtocell traffic in order to increase the cell throughput and also maximize the spectral efficiency over the FFR (Fractional Frequency Reuse) based conventional resource allocation schemes. Simulation Results show that the proposed scheme attains a bit similar SINR (Signal to Interference Noise Ratio) distribution but achieves much higher total cell throughput performance distribution over the conventional resource allocation schemes for FFR and future IEEE 802.16m based Femtocell network environment.

From 1820 4 times 4 binary matrices, 253 binary preprocessing matrices are designed for double space-time transmit diversity (DSTTD) systems with two 2 times 2 space-time block code (STBC) encoders. Among them, six matrices yielding the highest average minimum-post-processing SNR are proposed from numerical experimentation under uncorrelated channel conditions. The proposed preprocessing performs a superposition of the first and second (second and first) STBC symbols and a selection of two transmit antennas. Simulation results show that the proposed method provides 1.7 dB (1.8 dB) SNR improvement in uncorrelated (correlated) channel environment at 10-3 bit error rate over the conventional antenna shuffling method.

Performance analysis of multicell multiuser MIMO MC DS/CDMA system with MMSE user-ordered SIC technique

The theoretical error performance of double space time transmit diversity (DSTTD) system with optimum combining receiver is analyzed in this paper. By employing both spatial multiplexing and transmit diversity in one system, DSTTD provides practical tradeoff between system spectral efficiency and diversity gain. We derive exact analytical expressions to describe the symbol error rate for DSTTD systems. The effects of both diversity gain and antenna interference introduced by spatial multiplexing are quantified in the results. In addition, the performance of DSTTD system with successive interference cancellation is also investigated. Simulation results are in excellent agreement with the theoretical results obtained in this paper.

Most existing MIMO (multiput-input multiput-output) schemes optimize only either the diversity gain or the multiplexing gain. To obtain a good tradeoff between these two, the quasi-orthogonal group space-time (QoGST) architecture is proposed, wherein the transmit stream is subgrouped but encoded via an inter-group space-time block encoder, with group interference suppression at the receiver. This paper also considers another combined space-time coding and layered space-time architecture, which we refer to as group layered space-time (GLST), where space-time block coding is employed within each group. Under the assumption of Rayleigh fading and a prior perfect channel state information at the receiver, a performance analysis will demonstrate that both QoGST and GLST can achieve a good diversity-multiplexing tradeoff. QoGST is even superior to GLST. Simulation results will validate our analysis and further show that compared to the existent layered space-time block code (LSTBC) scheme, both QoGST and GLST can achieve a significant performance gain.

In this paper, we deal with the design of high-rate space-time block codes (STBCs) that achieve full-diversity with linear receivers which enable symbol-wise decoding. We propose three new high-rate coordinate interleaved STBCs and prove that they can achieve full-diversity with linear receivers for any optimally rotated square QAM constellation. Recently, Shang and Xia proved that the symbol rate of an STBC achieving full-diversity with a linear receiver is upper bounded by one complex information symbol per channel use (pcu). However, we show that with the use of coordinate interleaving, the proposed STBCs can exceed this upper bound to 4/3 complex information symbols pcu for two, three and four transmit antennas. For the symbol-by-symbol decoding of the proposed STBCs, we adapt the partial interference cancellation (PIC) group decoding algorithm recently proposed by Guo and Xia, and then further modify this decoder by applying successive interference cancellation (SIC) operation. Simulation results show that when linear receivers with minimum decoding complexity are used, the proposed STBCs achieve better error performance than their counterparts given in the literature.

Several Interference Cancellation (IC) schemes have been developed during this last decade for wireless networks to mitigate the effect of intra-network interferences, when each user is equipped with multiple antennas and employs Space Time Block Code (STBC) at transmission. However, these IC techniques all require multiple antennas at reception, which remains a challenge at the handset level due to cost and size limitations. In this context, the purpose of this paper is to develop Single Antenna IC (SAIC) techniques, and their Multiple antennas extensions (MAIC), to mitigate the effect of both intra-network and external interferences for users using both real-valued constellations, such as ASK constellations, and the Alamouti's scheme at transmission.

A double space-time transmit diversity (DSTTD) system employs four transmit antennas to multiplex two Alamouti space-time block code (STBC) units. In this letter, a specially-designed canceling mechanism is presented, which can efficiently separate the two STBC units for such systems. We show that the orthogonal structure, and so the merit of Alamouti STBC, can be kept. Compared with some previous interference cancelation methods, the proposed one requires much fewer floating-point operations (flops) while achieving similar error-rate performance.

In DS/CDMA systems, overcoming near/far effects and fading is imperative for satisfactory performance. One way to combat the near/far effect is to use stringent power control, as is done in most of the commercial systems. Another approach is Multi-User Detection (MUD). In addition to mitigating the near/far effect, MUD has the more fundamental potential of raising capacity by canceling Multiple Access Interference (MAI). This paper analyses the convergence behavior and performance of successive interference cancellation (SIC) for CDMA systems. This analysis will be generalized for Parallel Interference Cancellation (PIC) also. In this paper a Hybrid Interference Cancellation (HIC) receiver is designed by combining the successive and Parallel Interference Cancellation algorithms, so that the advantages of both the schemes are utilized effectively. The Hybrid Interference Cancellation scheme results in a simple, faster and reliable receiver. With the help of simulations, it is shown that this hybrid approach outperforms the other Multi-User Detection schemes.

To both eliminate interference from unrequested subfiles and improve sum degree-of-freedom (DoF) in multirelay Internet of vehicles (IoV) systems, a new decentralized multi-subsystem weighted interference cancellation (DMS-WIC) scheme with coded caching is proposed. It divides the transmission into two stages with optimized parameters to minimize link load. It also improves the sum DoF by jointly combining the weighted interference cancellation, orthogonal unicast, and decentralized coded multicast together. Given the number of interference-free subfiles larger than that of users, traditional interference cancellation wastes cache capacities of both users and relays by ignoring partial cache capacities and thus it fails to achieve a balance between the number of both users and interference cancellation subfiles. The DMS-WIC achieves additional DoF by adopting orthogonal unicast and subsequently dividing cache of both users and relays compared with those of traditional interference cancellation. In other cases, the weighted requested subfiles are transmitted by combining physical layer file division and network layer coding delivery together to achieve interference alignment and cancellation gains. The DMS-WIC adaptively adjusts files and subsystem partition parameters by perceiving systematical parameters. Besides, a multirelay cooperative coded caching is introduced to further reduce transmission and complexity. Given the number of relays larger than that of users, the relays deliver coded subfiles with different user sets. Otherwise, a relay skips the fix of the user number units, until all user sets are taken after the completion of a transmission. Simulation results show that the proposed DMS-WIC with coded caching achieves more than 10.6% sum DoF gain compared with that of traditional interference cancellation.

In this work, group‐wise successive interference cancellation (GSIC) scheme for multi‐rate CDMA systems is proposed. A multi‐rate CDMA system is a CDMA system that can support voice users together with data users which may have different data rates. In the proposed group‐wise detection, users with the same information rate are grouped and detected together. Users with the highest information rate are detected first, neglecting the presence of the other users in the system. Interference between the groups is cancelled in a successive order. The proposed scheme is based on the minimum mean square error (MMSE) criterion. We also studied the decision feedback interference cancellation for multi‐rate CDMA systems. The performance of the proposed detection scheme is compared with that of conventional detector, the decorrelating detector, and the linear MMSE detector for multi‐rate CDMA systems. The proposed scheme achieves better performance than the above‐mentioned detectors. The proposed scheme also provides significantly high spectral efficiency under certain conditions. The algorithms in the proposed scheme are suitable for both terrestrial and satellite applications of multi‐rate CDMA systems. Copyright © 2003 John Wiley &amp; Sons, Ltd.

In this paper, we propose a spatially modulated space-time block coding scheme, called DT-SM, by combining the conventional double space time transmit diversity (DSTTD) with spatial modulation. First, we design a set of four basic spatial constellation (SC) codewords and an extended set of 16 SC codewords for four transmit antennas by using computer search based on the rank and determinant criterion. We then present a generalized algorithm to design SC codewords for an arbitrary number of transmit antennas greater than four. Compared with DSTTD, the proposed scheme attains the same transmit diversity order, while offering higher spectral efficiency. Besides, we derive a union bound for the bit error rate (BER) of the proposed DT-SM scheme in a quasi-static Rayleigh fading channel with spatial correlation. In order to achieve the performance of maximum-likelihood (ML) estimation at reduced detection complexity, we develop a sphere decoder based on the conventional Schnorr-Euchner sphere decoder. BER performance and detection complexity of the DT-SM scheme are evaluated by computer simulations. It is shown that the proposed DT-SM outperforms many existing MIMO and SM-based MIMO schemes at reasonable detection complexity, even in correlated MIMO channels.

We consider an asynchronous two-way relay network in which a few distributed relays assist in the communication between two single-antenna terminals through analog network coding. The asynchronous transmission between relays and terminals causes symbol misalignments and results in diversity loss in space–time codes (STCs). We propose a family of zero-padded time-reversal STC that can achieve full diversity with low-complexity maximum likelihood (ML) decoding, given a bound for the path delay difference. With ML decoding, the proposed code is decomposed into several independent parts, which greatly facilitate the decoding process. For two-relay scenarios, three code designs based on Alamouti code, quasi-orthogonal space–time block code, and multigroup decodable STC are provided for each relay with one, two, and four antennas, respectively. For three-relay scenarios, one code design based on quasi-orthogonal space-time block code is provided for each relay with one antenna. Proof of full diversity is established, and the decoding complexity order is analyzed for all four designs. Simulations confirm the full diversity gain of all designs. The bit-error-rate performance in asynchronous scenarios is almost similar to that in synchronous scenarios.

Recently, space-time block coded OFDM (ST-OFDM), that applies space-time block codes (STBC) to OFDM, has been proposed. Space-frequency block coded OFDM (SF-OFDM) has also been proposed, where the block codes are formed over the space and frequency domain. ST-OFDM and SF-OFDM achieve good performance over multipath fading environments and fast fading environments, respectively. For systems with two transmit antennas, orthogonal conditions are required to separate the received signals: in ST-OFDM, the frequency responses of two consecutive OFDM symbols are almost identical; in SF-OFDM, the frequency responses of two adjacent subcarriers are almost identical. In practical fading environments, however, these orthogonality conditions sometimes cannot be satisfied. In those environments, the received signals cannot be well separated and the performances are degraded. Recently, a new zero-forcing (ZF) diagonalized maximum likelihood decoder (DMLD) was proposed for the space-time block coded single carrier QPSK system to maintain the orthogonality of STBC under fast fading environments and flat fading environments; the channel separation in DMLD is performed by the ZF algorithm using two receive signals at time index 2n, 2n+1 (STC) or two subcarriers (SFC). The matrix generated after the channel separation is not an identity matrix, but a matrix proportional to an identity matrix. We show that ST/SF-OFDM with DMLD outperform ST/SF-OFDM in terms of bit error rate (BER).