Recent advancements in iterative processing of channel codes and the development of turbo codes have allowed the communications industry to achieve near-capacity on a single-antenna Gaussian or fading channel with low complexity. We show how these iterative techniques can also be used to achieve near-capacity on a multiple-antenna system where the receiver knows the channel. Combining iterative processing with multiple-antenna channels is particularly challenging because the channel capacities can be a factor of ten or more higher than their single-antenna counterparts. Using a "list" version of the sphere decoder, we provide a simple method to iteratively detect and decode any linear space-time mapping combined with any channel code that can be decoded using so-called "soft" inputs and outputs. We exemplify our technique by directly transmitting symbols that are coded with a channel code; we show that iterative processing with even this simple scheme can achieve near-capacity. We consider both simple convolutional and powerful turbo channel codes and show that excellent performance at very high data rates can be attained with either. We compare our simulation results with Shannon capacity limits for ergodic multiple-antenna channel.

http://www.ece.ualberta.ca/~hcdc/Library/StCommClass/HocTen01.pdf

Achieving near-capacity on a multiple-antenna channel

Matrix Differential Calculus with Applications in Statistics and Econometrics

It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.

/pdf/an-overview-of-limited-feedback-in-wireless-communication-1njp2bb1kz.pdf

An overview of limited feedback in wireless communication systems

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area.

/pdf/principles-of-physical-layer-security-in-multiuser-wireless-3w4jvwpgy4.pdf

Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

Digital Coding of Waveforms

In this paper we consider the secure transmission with multiple-input, single-output, single-antenna eavesdropper (MISOSE) in fast fading channels where the transmitter knows perfect legitimate channel state information but only the statistics of the eavesdropper's channel. For the MISOSE channels, the artificial noise assisted beamforming proposed by Goel and Negi is a promising technique, where the artificial noise is imposed on the null space of the legitimate channel to disrupt the eavesdropper's reception. Here we propose a generalized artificial noise scheme which allows the injection of the artificial noise to the legitimate channel. Although the generalized artificial noise may cause the leakage of artificial noise at the legitimate receiver, the secrecy rate can still be improved since the covariance matrix of it is more flexible than the heuristic one selected by Goel and Negi. To fully characterize the proposed scheme, we investigate the optimization of its secrecy rate. We first derive the conditions under which the beamformers of the message bearing signal and the generalized artificial noise being the same is optimal. Based on this choice, the complicated secrecy rate optimization problem over the covariance matrices of the message-bearing signal and the generalized artificial noise can be reduced to a much simpler power allocation problem. We also develop an efficient algorithm to solve this non-convex power allocation problem. Numerical results show that our generalized artificial noise scheme outperforms Goel and Negi's heuristic selection, especially in the near eavesdropper settings. In particular, with the aid of the proposed scheme, the regime with non-zero secrecy rate is enlarged, which can significantly improve the connectivity of the network.

On Secrecy Rate of the Generalized Artificial-Noise Assisted Secure Beamforming for Wiretap Channels

In this paper, a point-to-point orthogonal-frequency- division multiplexing (OFDM) system with a decode-and- forward (DF) relay is considered. The transmission consists of two hops. The source transmits in the first hop, and the relay transmits in the second hop. Each hop occupies one time slot. The relay is half-duplex, and capable of decoding the message on a particular subcarrier in one time slot, and re-encoding and forwarding it on a different subcarrier in the next time slot. Thus, each message is transmitted on a pair of subcarriers in two hops. It is assumed that the destination is capable of combining the signals from the source and the relay pertaining to the same message. The goal is to maximize the weighted sum rate of the system by jointly optimizing subcarrier pairing and power allocation on each subcarrier in each hop. The weighting of the rates is to take into account the fact that different subcarriers may carry signals for different services. Both total and individual power constraints for the source and the relay are investigated. For the situations where the relay does not transmit on some subcarriers because doing so does not improve the weighted sum rate, we further allow the source to transmit new messages on these idle subcarriers. To the best of our knowledge, such a joint optimization inclusive of the destination combining has not been discussed in the literature. The problem is first formulated as a mixed integer programming problem. It is then transformed to a convex optimization problem by continuous relaxation, and solved in the dual domain. Based on the optimization results, algorithms to achieve feasible solutions are also proposed. Simulation results show that the proposed algorithms almost achieve the optimal weighted sum rate and outperform the existing methods in various channel conditions.

Joint Subcarrier Pairing and Power Allocation for OFDM Transmission With Decode-and-Forward Relaying

In attempting to find a spectrally and power efficient channel code which is able to exploit maximum diversity from a wireless channel whenever available, we investigate the possibility of constructing a full antenna diversity space-time turbo code. As a result, both three-antenna and two-antenna (punctured) constructions are shown to be possible and very easy to find. To check the decodability and performance of the proposed codes, we derive non-binary soft-decoding algorithms. The performance of these codes are then simulated and compared with two existing space-time convolutional codes (one has minimum worst-case symbol-error probability; the other has maximal minimum free distance) having similar decoding complexity. As the simulation results show, the proposed space-time turbo codes give similar or slightly better performance than the convolutional codes under extremely slow fading. When fading is fast, the better distance spectra of the turbo codes help seize the temporal diversity. Thus, the performance advantage of the turbo codes becomes evident. In particular, 10/sup -5/ bit-error rate and 10/sup -3/ frame-error rate can be achieved at less than 6-dB E/sub b//N/sub 0/ with 1 b/s/Hz and binary phase-shift keying modulation. The practical issue of obtaining the critical channel state information (CSI) is also considered by applying an iteratively filtered pilot symbol-assisted modulation technique. The penalty when the CSI is not given a priori is about 2-3 dB.

Space-time turbo codes with full antenna diversity

In an embodiment, a composite signaling message part is formed to include at least two segments, each segment including data identifying a different user equipment (UE). In another embodiment, a different portion of a composite signaling message part is transmitted over at least one same time slot in each of the shared control channels; the part including at least two segments and each segment including data identifying a different user equipment (UE). In these embodiments, the part further includes a cyclic redundancy code (CRC) generated by jointly encoding the at least two segments. In a further aspect of the method, more than one shared control channel jointly carrying a signaling message are power controlled such that each shared control channel carrying more data associated with one of the UEs is power controlled in accordance with that UE. In a still further embodiment, the channelized code information for a dedicated control channel is divided between first and second parts of the shared control signals.

Shared signaling for multiple user equipment

Errors in closed loop transmit diversity (CLTD) feedback signaling may be detected and/or corrected by a mobile station, according to aspects of the present invention, based on signals received from a base station. The mobile station is generally configured to compute antenna weights to be applied at the base station and feed back corresponding antenna control bits to the base station, as in conventional CLTD systems. However, rather than automatically process subsequent transmissions received from the base station as if the base station properly received the antenna control bits and applied the computed antenna weights, the mobile station attempts to determine the antenna weights actually applied at the base station, and uses these determined antenna weights for processing the subsequent transmissions. Accordingly, even if a feedback signaling error occurred, resulting in the base station using the wrong antenna weights, the mobile station may properly process the transmissions. According to some aspects of the present invention, the base station transmits (feeds forward) antenna control bits actually received from the mobile station on a feed forward channel, and the mobile station processes subsequent transmissions using antenna weights generated based on the fed forward antenna control bits.

Hsuan-Jung Su

Papers

On Secrecy Rate of the Generalized Artificial-Noise Assisted Secure Beamforming for Wiretap Channels

Joint Subcarrier Pairing and Power Allocation for OFDM Transmission With Decode-and-Forward Relaying

Space-time turbo codes with full antenna diversity

Shared signaling for multiple user equipment

Method and apparatus for feedback error detection in a wireless communications systems