Duality between channel capacity and rate distortion with two-sidedstate information

We show that the duality between channel capacity and data compression is retained when state information is available to the sender, to the receiver, to both, or to neither. We present a unified theory for eight special cases of channel capacity and rate distortion with state information, which also extends existing results to arbitrary pairs of independent and identically distributed (i.i.d.) correlated state information (S₁, S₂) available at the sender and at the receiver, respectively. In particular, the resulting general formula for channel capacity C = max_p(u,x|s₁) [I(U; S₂, Y) I(U; S₁)] assumes the same form as the generalized Wyner-Ziv (1976) rate distortion function R(D) = min_p(u|x, s₁)p(x&capped;|u, s₂) [I(U; S ₁, X) 1(U; S₂)]     

基于五粒子团簇态实现四粒子团簇态的概率隐形传态

为实现更经济的四粒子团簇态的概率隐形传输,提出了一种利用五粒子团簇态为量子信道的隐形传态方案.基于解纠缠-隐形传输-重构纠缠方法,发送者在发送信息之前对信息态进行一次控制非门操作和投影测量,将解纠缠的信息发送给接收者.在这个过程中发送者需要进行2次Bell基联合测量和1次单粒子测量,接收者根据发送者的测量结果进行相应操作,得出解纠缠的信息态.引入辅助粒子重构原始的未知信息态,信息传输成功的概率为4|a|2,提出的方案可以很好地应对一般窃听方式.     

Capacity of nearly decomposable Markovian fading channels under asymmetric receiver-sender side information

We investigate the following issue: if fast fades are Markovian and known at the receiver, while the transmitter has only a coarse quantization of the fading process, what capacity penalty comes from having the transmitter act on the current coarse quantization alone? For time-varying channels which experience rapid time variations, sender and receiver typically have asymmetric channel side information. To avoid the expense of providing, through feedback, detailed channel side information to the sender, the receiver offers the sender only a coarse, generally time-averaged, representation of the state of the channel, which we term slow variations. Thus, the receiver tracks the fast variations of the channel (and the slow ones perforce) while the sender receives feedback only about the slow variations. While the fast variations (micro-states) remain Markovian, the slow variations (macro-states) are not. We compute an approximate channel capacity in the following sense: each rate smaller than the "approximate" capacity, computed using results by Caire and Shamai, can be achieved for sufficiently large separation between the time scales for the slow and fast fades. The difference between the true capacity and the approximate capacity is O(/spl epsi/log/sup 2/(/spl epsi/)log(-log(/spl epsi/))), where /spl epsi/ is the ratio between the speed of variation of the channel in the macro- and micro-states. The approximate capacity is computed by power allocation between the slowly varying states using appropriate water filling.     

A new adaptive receiver-initiated scheme for mitigating starvation in wireless networks

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) has been adopted by the IEEE 802.11 standard and provides good performance when all transmitters are within the range of each other. Unfortunately, in multi-hop topologies, the asymmetric view of the channel state leads to a throughput distribution where a few flows may capture all the available bandwidth while many other flows get very low throughput and sometime meet starvation. To address this problem, in this paper we describe a solution called Carrier Sense Multiple Access with Collision Avoidance by Receiver Detection (CSMA/CARD) which makes use of collisions sensed by a receiver at the physical layer to help the handshake mechanism and mitigate the effect of such problem. More specifically, we propose a mechanism based on historical observations, where collisions can be used by the receiver to predict whether some sender attempted to initiate a transmission. The receiver then reacts accordingly by participating itself in a handshake sequence. We show some interesting results, obtained through analysis and simulations, when the CSMA/CARD is compared to the IEEE 802.11 protocol.     

RT Oblivious Erasure Correcting

An erasure correcting scheme is rateless if it is designed to tolerate any pattern of packet loss and reveal the transmitted information after a certain number of packets is received. On the one hand, transmission schemes that use rateless erasure correcting schemes do not usually use a feedback channel. However, they may require significant amount of additional processing by both the sender and the receiver. On the other hand, automatic repeated request protocols use a feedback channel to assist the sender, and do not usually require information processing. In this work we present a combined approach, where a lean feedback channel is used to assist the sender to efficiently transmit the information. Our Real-Time oblivious approach minimizes the processing time and the memory requirements of the receiver and, therefore, fits a variety of receiving devices. In addition, the transmission is real-time where the expected number of original packets revealed when a packet is received is approximately the same throughout the entire transmission process. We use our end-to-end scheme as a base for broadcast (and multicast) schemes. An overlay tree structure is used to convey the information to a large number of receivers. Moreover, the receivers may download the information from a number of senders or even migrate from one sender to another.     

A periodic state exchange protocol and its verification

We present an elegant protocol for reliably transmitting data messages from a sender to a receiver over a highspeed network that may reorder, lose, or corrupt messages. The protocol is based on a new principle that calls for the periodic exchange of state information between the sender and receiver. Our formal definition of the protocol is abstract and does not include explicit timing information such as the rate of sending state information. The abstract definition makes our formal verification of the protocol simple and based solely on well-established concepts: invariants, well-foundedness, and action fairness. We use the formal definition of the protocol and its proof of correctness to deduce the required timing information. In particular, we show that the rate of sending state information is at most (m-1)/2T where m is a measure of the memory size in the sender, and T is an upper bound on the required time for one message to be sent, propagated, and received between the sender and receiver     

iMAC: improved Medium Access Control for multi‐channel multi‐hop wireless networks

Trends in wireless networks are increasingly pointing towards a future with multi‐hop networks deployed in multi‐channel environments. In this paper, we present the design for iMAC—a protocol targeted at Medium Access Control in such environments. iMAC uses control packets on a common control channel to facilitate a three‐way handshake between the sender and the receiver for every packet transmission. This handshake enables the sender and the receiver to come to a consensus on a channel to use for data transmission and also signals to neighboring nodes about the contention on that channel. iMAC then uses a mechanism similar to 802.11 for data communication. Our evaluation of iMAC shows that it provides significant gains in throughput in comparison with uninformed channel selection, especially when contention for channel bandwidth is neither too low nor too high; intelligent selection of channels by iMAC is necessary to harness available bandwidth resources in the presence of medium levels of contention. Copyright © 2011 John Wiley & Sons, Ltd.     

A dual-driven adaptive video system over WLAN

This paper proposes a dual-driven adaptive (D2D-Adap) video server system over wireless local area network (WLAN). In the system, the status of the wireless channel is monitored at the sender side, And at the receiver side. the packet loss rate, delay etc. are measured and fed back to the sender. The status information from both sides is used to adapt the encoding and transmission rate of the video in the server. The adaptation scheme in the proposed system can estimate the network channel situation accurately and quickly and can provide better video communication service over WLAN. The simulation and test results show that the proposed system can respond to the changes of the wireless channel quickly and therefore provide smoother video to clients.     

Joint channel estimation and resource allocation for MIMO systems-part I: single-user analysis

Multiple antenna systems are known to provide very large data rates, when the perfect channel state information (CSI) is available at the receiver. However, this requires the receiver to perform a noise-free, multi-dimensional channel estimation, without using communication resources. In practice, any channel estimation is noisy and uses system resources. We shall examine the trade-off between improving channel estimation and increasing the achievable data rate. We consider transmitside correlated multi-input multi-output (MIMO) channels with block fading, where each block is divided into training and data transmission phases. The receiver has a noisy CSI that it obtains through a channel estimation process, while the transmitter has partial CSI in the form of covariance feedback. In Part I of this two-part paper, we consider the single-user case, and optimize the achievable rate jointly over parameters associated with the training phase and data transmission phase. In particular, we first choose the training signal to minimize the channel estimation error, and then, develop an iterative algorithm to solve for the optimum system resources such as time, power and spatial dimensions. Specifically, the algorithm finds the optimum training duration, the optimum allocation of power between training and data transmission phases, the optimum allocation of power over the antennas during the data transmission phase.     

A differential detection scheme for transmit diversity

We present a transmission scheme for exploiting diversity given by two transmit antennas when neither the transmitter nor the receiver has access to channel state information. The new detection scheme can use equal energy constellations and encoding is simple. At the receiver, decoding is achieved with low decoding complexity. The transmission provides full spatial diversity and requires no channel state side information at the receiver. The scheme can be considered as the extension of differential detection schemes to two transmit antennas     

Adaptive Coding and Modulation for Multicast Transmission in Packet Radio Networks

A low-complexity protocol is described and evaluated for adaptation of the modulation and coding for multicast transmission in half-duplex packet radio networks. The adaptive multicast transmission protocol is designed to compensate for changes in propagation conditions that occur from packet to packet during a session with one sender and multiple receivers. The protocol relies on simple receiver statistics to obtain the control information for adapting the modulation and coding, and it also provides scheduling to avoid collisions among acknowledgments from the receivers. The throughput provided by the protocol is compared with performance results for hypothetical ideal adaptive multicast transmission protocols that are given perfect channel state information. We illustrate the importance of adaptive modulation and channel coding in systems that employ fountain coding for packet erasure correction.     

Channel estimation techniques for linear precoded systems: Supervised, unsupervised, and hybrid approaches

Linear precoding is an attractive technique to combat interference in multiple-input multiple-output systems because it reduces cost and power consumption at the receiver. Frequency division duplex systems with linear precoding acquire the channel state information at the receiver side by using supervised algorithms. Such methods make use of pilot symbols periodically provided by the transmitter. Next, this channel state information is sent to the transmitter side through a low-cost feedback channel. Thus, the available channel information allows the transmitter to adapt signals to the channel conditions. Given that pilot symbols do not convey user data, they penalize throughput, spectral efficiency, and transmission energy consumption of the system. In this work, we propose to mitigate the aforementioned limitations by combining both supervised and unsupervised algorithms to acquire the channel state information needed by the transmitter. The key idea consists in introducing a simple criterion to determine whether the channel has suffered a significant variation which requires the transmission of pilot symbols. Otherwise, when small fluctuations happen, an unsupervised method is used to track these channel variations instead. This criterion will be evaluated by considering two types of strategies for the design of the linear precoders: Zero-Forcing and Wiener criteria.     

四粒子W态的概率隐形传态

提出利用两个二粒子非最大纠缠态作为量子信道传送任意四粒子W纠缠态的方案。发送者只需做一次正交完备基测量, 然后通过经典信道将测量结果告知接收者,接受者通过引入辅助粒子F,并在适当的么正变换后做Von Neumann测量, 接着引入辅助粒子B3B4,并对手中拥有的粒子进行再一次的幺正变换,就能以一定的概率完成四粒子纠缠态的隐形传输。整个隐形传态过程中,发送者只需一次正交完备基测量,且当量子信道为最大纠缠态时,此方案可实现完全传输。     

Binary adaptive coded pilot symbol assisted modulation over Rayleigh fading channels without feedback

Pilot symbol assisted modulation (PSAM) is a standard approach for transceiver design for time-varying channels, with channel estimates obtained from pilot symbols being employed for coherent demodulation of the data symbols. In this paper, we show that PSAM schemes can be improved by adapting the coded modulation strategy at the sender to the quality of the channel measurement at the receiver, without requiring any channel feedback from the receiver. We consider performance in terms of achievable rate for binary signaling schemes. The transmitter employs interleaved codes, with data symbols coded according to their distance from the nearest pilot symbols. Symbols far away from pilot symbols encounter poorer channel measurements at the receiver and are therefore coded with lower rate codes, while symbols close to pilot symbols benefit from recent channel measurements and are coded with higher rate codes. The performance benefits from this approach are quantified in the context of binary signaling over time-varying Rayleigh fading channels described by a Gauss-Markov model. The spacing of the pilot symbols is optimized to maximize the mutual information between input and output in this setting. Causal and noncausal channel estimators of varying complexity and delay are considered. It is shown that, by appropriate optimization for the spacing between consecutive pilot symbols, the adaptive coding techniques proposed can improve achievable rate, without any feedback from the receiver to the sender. Moreover, channel estimation based on the two closest pilot symbols is generally close to optimal.     

Capacity/Throughput Optimization for H-BLAST with SC Receiver over MIMO Channels

Among various Bell Labs layered space-time (BLAST) architectures over multiple input multiple output (MIMO) channels, we focus on the horizontal BLAST (H- BLAST) transmission scheme as it can achieve the channel capacity with a simple receiver, namely the successive cancellation (SC) receiver. The power optimization across layers is considered with a short-term power constraint. In addition, for block- fading channels, the rate optimization across layers is studied to maximize the throughput when the instantaneous channel state information (CSI) is not available. Since the CSI is not available, the rates can be greater than the instantaneous channel capacity and error propagation in the SC receiver is inevitable. Thus, the rate optimization plays a key role in reducing the chance of error propagation to maximize the throughput. It is shown that the optimal rates can be obtained recursively and each optimization can be carried out by a one-dimensional search.     

Optimal Cross-Layer Scheduling of Transmissions Over a Fading Multiaccess Channel

We consider the problem of several users transmitting packets to a base station, and study an optimal scheduling formulation involving three communication layers, namely, the medium access control, link, and physical layers. We assume Markov models for the packet arrival processes and the channel gain processes. Perfect channel state information is assumed to be available at the transmitter and the receiver. The transmissions are subject to a long-run average transmitter power constraint. The control problem is to assign power and rate dynamically as a function of the fading and the queue lengths so as to minimize a weighted sum of long run average packet transmission delays.     

Practical robust uniform channel decomposition scheme for CSI mismatch in limited feedback MIMO systems

Uniform channel decomposition (UCD) has been proven to be optimal in bit error rate (BER) performance and strictly capacity lossless when perfect channel state information (CSI) is assumed to be available at both the transmitter and receiver side. In practice, CSI can be obtained by channel estimation at receiver and conveyed to transmitter via a limited-rate feedback channel. In such case, the implementation of traditional UCD by treating the imperfect CSI as perfect CSI cause significant performance degradation due to inevitable channel estimation error and vector quantization error. To overcome this problem, a practical robust UCD scheme was proposed in this paper, which includes two steps, firstly, a matching architecture was proposed to eliminate the mismatch between CSI at receiver (CSIR) and CSI at transmitter (CSIT), secondly, an MMSE based robust UCD scheme considering channel estimation error and vector quantization error as an integral part of the design was derived. Simulation results show that the proposed practical robust UCD scheme is capable of improving the BER performance greatly in the context of channel estimation error and vector quantization error compared with the traditional UCD scheme.     

Upper and Lower Bounds on Black-Box Steganography

We study the limitations of steganography when the sender is not using any properties of the underlying channel beyond its entropy and the ability to sample from it. On the negative side, we show that the number of samples the sender must obtain from the channel is exponential in the rate of the stegosystem. On the positive side, we present the first secret-key stegosystem that essentially matches this lower bound regardless of the entropy of the underlying channel. Furthermore, for high-entropy channels, we present the first secret-key stegosystem that matches this lower bound statelessly (i.e., without requiring synchronized state between sender and receiver). Preliminary version appears in TCC 2005 [5].     

利用智能天线实现多点中继功能的Ad Hoc网络MAC协议

在Ad Hoc网络中,采用多跳传输来提高数据传输的质量以及速率。传统的单中继节点已经不能适应迅速增大的数据量以及节点的移动造成的信道衰落情况,所以本文提出了基于智能天线实现多点中继的MAC协议,该协议采用了智能天线实现了菱形握手机制,使数据实现同步传输。其次采用空时编码的协作机制,通过估计源信号来防止中继节点与目的节点信道衰落的情况。最后利用Busy Tones解决了隐藏终端和暴露终端的问题。通过仿真与比较证明MRDMAC协议在数据延时和通过率等各个方面都有很大的优越性。