Search

A multiple-input multiple-output (MIMO) version of the dirty paper channel is studied, where the channel input and the dirt experience the same fading process, and the fading channel state is known at the receiver. This represents settings where signal and interference sources are co-located, such as in the broadcast channel. First, a variant of Costa’s dirty paper coding is presented, whose achievable rates are within a constant gap to capacity for all signal and dirt powers. In addition, a lattice coding and decoding scheme is proposed, whose decision regions are independent of the channel realizations. Under Rayleigh fading, the gap to capacity of the lattice coding scheme vanishes with the number of receive antennas, even at finite Signal-to-Noise Ratio (SNR). Thus, although the capacity of the fading dirty paper channel remains unknown, this paper shows it is not far from its dirt-free counterpart. The insights from the dirty paper channel directly lead to transmission strategies for the two-user MIMO broadcast channel, where the transmitter emits a superposition of desired and undesired (dirt) signals with respect to each receiver. The performance of the lattice coding scheme is analyzed under different fading dynamics for the two users, showing that high-dimensional lattices achieve rates close to capacity. [ABSTRACT FROM PUBLISHER]

The sum capacity of a Gaussian broadcast MIMO channel can be achieved with dirty paper coding (DPC). However, algorithms that approach the DPC sum capacity do not appear viable in the forseeable future, which motivates lower complexity interference suppression techniques. Block diagonalization (BD) is a linear preceding technique for downlink multiuser MIMO systems. With perfect channel knowledge at the transmitter, BD can eliminate other users' interference at each receiver. In this paper, we study the sum capacity of BD with and without receive antenna selection. We analytically compare BD without receive antenna selection to DPC for a set of given channels. It is shown that (1) if the user channels are orthogonal to each other, then BD achieves the same sum capacity as DPC; (2) if the user channels lie in the same subspace, then the gain of DPC over BD can be upper bounded by the minimum of the number of transmit and receive antennas. These observations also hold for BD with receive antenna selection. Further, we study the ergodic sum capacity of BD with and without receive antenna selection in a Rayleigh fading channel. Simulations show that BD can achieve a significant part of the total throughput of DPC. An upper bound on the ergodic sum capacity gain of DPC over BD is proposed for easy estimation of the gap between the sum capacity of DPC and BD without receive antenna selection. [ABSTRACT FROM PUBLISHER]

This paper proposes new limited-feedback Channel State Information (CSI) calculation schemes for Zero Forcing (ZF)-precoded downlink Multi-User Multiple-Input Multiple-Output (MU-MIMO) systems. It is a common understanding that the feedback quantized by the codebook limits the performance of MU-MIMO. In this paper, through a quasi-ZF or a quasi-Minimum Mean-Squared Error (MMSE) weight, the channel matrix is transferred to one of the codebook vectors, based on which, the CSI is calculated. Thus, the quantization error is minimized. Meanwhile, the selection for the codebook vector guarantees the maximizing of the estimated Signal to Interference plus Noise Ratio (SINR). We verify that the proposed scheme obtains accurate feedback information, and the predicted weight can be the same as the optimal linear decoder as if the receiver knew all the precoder information that is fed-forward from the BS, as long as the number of antennas for each receiver equals that for the transmitter, and equals that for the total transmit data streams. Compared to the commonly used Precoding Matrix Index (PMI) based method, which uses rank-one single user (SU)-MIMO feedback, simulation results show that the proposed schemes achieve higher sum capacities in different scenarios. Moreover, since the weight can be directly used as the decoder, the feed-forward overhead is reduced. [ABSTRACT FROM PUBLISHER]

Broadcast (or point to multipoint) communication has attracted a lot of research recently. In this paper, we consider the group broadcast channel where the users' pool is divided into groups, each of which is interested in common information. Such a situation occurs for example in digital audio and video broadcast where the users are divided into various groups according to the shows they are interested in. The paper obtains upper and lower bounds for the sum rate capacity in the large number of users regime and quantifies the effect of spatial correlation on the system capacity. The paper also studies the scaling of the system capacity when the number of users and antennas grow simultaneously. It is shown that in order to achieve a constant rate per user, the number of transmit antennas should scale at least logarithmically in the number of users. [ABSTRACT FROM PUBLISHER]

This paper studies linear transmit filter design for Weighted Sum-Rate (WSR) maximization in the multiple input multiple output broadcast channel (MIMO-BC). The problem of finding the optimal transmit filter is non-convex and intractable to solve using low complexity methods. Motivated by recent results highlighting the relationship between mutual information and minimum mean square error (MMSE), this paper establishes a relationship between weighted sum-rate and weighted MMSE in the MIMO-BC. The relationship is used to propose two low complexity algorithms for finding a local weighted sum-rate optimum based on alternating optimization. Numerical results studying sum-rate show that the proposed algorithms achieve high performance with few iterations. [ABSTRACT FROM PUBLISHER]

In recent years, the research on multiple-input multiple-output (MIMO) broadcast channels has attracted much interest, especially since the discovery of the broadcast channel capacity achievable through the use of dirty paper coding (DPC). In this paper, we propose a new matrix decomposition, called the block diagonal geometric mean decomposition (BD-GMD), and develop transceiver designs that combine DPC with BD- GMD for MIMO broadcast channels. We also extend the BD- GMD to the block diagonal uniform channel decomposition (BD- UCD) with which the MIMO broadcast channel capacity can be achieved. Our proposed schemes decompose each user's MIMO channel into parallel subchannels with identical SNRs/SINRs, thus equal-rate coding can be applied across the subchannels of each user. Numerical simulations show that the proposed schemes demonstrate superior performance over conventional schemes. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary. [ABSTRACT FROM PUBLISHER]

We consider the content delivery problem in a fading multi-input single-output channel with cache-aided users. We are interested in the scalability of the equivalent content delivery rate when the number of users, $K$ , is large. Analytical results show that, using coded caching and wireless multicasting, without channel state information at the transmitter, linear scaling of the content delivery rate with respect to $K$ can be achieved in some different ways. First, if the multicast transmission spans over $L$ independent sub-channels, e.g., in quasi-static fading if $L = 1$ , and in block fading or multi-carrier systems if $L>1$ , linear scaling can be obtained, when the product of the number of transmit antennas and the number of sub-channels scales logarithmically with $K$ . Second, even with a fixed number of antennas, we can achieve the linear scaling with a threshold-based user selection requiring only one-bit feedbacks from the users. When CSIT is available, we propose a mixed strategy that combines spatial multiplexing and multicasting. Numerical results show that, by optimizing the power split between spatial multiplexing and multicasting, we can achieve a significant gain of the content delivery rate with moderate cache size. [ABSTRACT FROM PUBLISHER]

Precoding with block diagonalization (BD) is an attractive technique for approaching the sum capacity in the multiuser multiple-input multiple-output (MIMO) broadcast channel. Unfortunately, BD requires either global channel state information at every receiver or an additional training phase, which demands additional control overhead and additional system planning. In this paper we propose a new multiuser MIMO algorithm that combines BD with vector perturbation (VP). The proposed algorithm avoids the second training phase, reduces each user is receiver complexity thanks to pre-equalization with VP at the transmitter, and has comparable diversity performance to BD with maximum likelihood decoding algorithm. A bound on the achievable sum rate for the proposed technique is derived and used to show that BD with VP approaches the achievable sum rate of BD with water-filling. Numerical simulations confirm that the proposed technique provides better bit error rate and diversity performance than BD with a zero-forcing receiver as well as BD with zero-forcing precoding. [ABSTRACT FROM PUBLISHER]

Orthogonal random beamforming (ORB) constitutes a mean to exploit spatial multiplexing and multi-user diversity (MUD) gains in multi-antenna broadcast channels. To do so, as many random beamformers as transmit antennas (M) are generated and on each beam the user experiencing the most favorable channel conditions is scheduled. Whereas for a large number of users the sum-rate of ORB exhibits an identical growth rate as that of dirty paper coding, performance in sparse networks (or in networks with an uneven spatial distribution of users) is known to be severely impaired. To circumvent that, in this paper we modify the scheduling process in ORB in order to select a subset out of the M available beams. We propose several beam selection algorithms and assess their performance in terms of sum-rate and aggregated throughput (i.e., rate achieved with practical modulation and coding schemes), along with an analysis of their computational complexity. Since ORB schemes require partial channel state information (CSI) to be fed back to the transmitter, we finally investigate the impact of CSI quantization on system performance. More specifically, we prove that most of the MUD can be still exploited with very few quantization bits and we derive a beam selection approach trading-off system performance vs. feedback channel requirements. [ABSTRACT FROM PUBLISHER]

Block diagonalization is one approach for linear preceding in the multiple-input multiple-output broadcast channel that sends multiple interference free data streams to different users in the same cell. Unfortunately, block diagonalization neglects other-cell interference (OCI), which limits the performance of users at the edge of the cell. This paper presents an OCI-aware enhancement to block diagonalization that uses a whitening filter for interference suppression at the receiver and a novel precoder using the interference-plus-noise covariance matrix for each user at the transmitter. For complex Gaussian matrix channels, the asymptotic sum rate of the proposed system is analyzed under a large antenna assumption for isotropic inputs and compared to conventional block diagonalization. The capacity loss due to OCI is quantified in terms of results from single-user MIMO capacity. Several numerical examples compare achievable sum rates, the proposed asymptotic rates, and the capacity loss, in low and high interference regimes. [ABSTRACT FROM PUBLISHER]

This paper investigates the capacity of multiple- access and broadcast channels with MIMO-MRC systems in spatially correlated environments. We present new capacity approximations which are shown to be accurate. The approximations are based on new simple expansions which we derive for the maximum eigenvalue distribution of correlated Wishart matrices. We then proceed to analyze the affects of correlation and show it is beneficial for capacity. Our results are confirmed through comparison with Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

Scheduling in a broadcast channel based on partial channel-state-information at the transmitter is carried out in an opportunistic way. In this paper, the number of generated beams is larger than the number of available base station antennas, where the beams are obtained through Grassmannian line packing to guarantee the largest orthogonality among them. Approximate expressions and bounds are derived for the sum capacity of the proposed approach together with its scaling law. For practical systems, we show that this scheme can increase the number of serviced users under a minimum-rate-per-user requirement. [ABSTRACT FROM PUBLISHER]

This paper introduces extensions for the broadcast approach for a multi-input multi-output (MIMO) block fading channel, with receiver only channel state information (CSI). Previous works have not been able to fully characterize the fundamental MIMO broadcasting upper bound. As it seems that analytical solution for this problem is quite difficult to achieve, we consider here sub-optimal schemes, for which achievable rates may be computed. In particular, finite level coding over a MIMO channel instead of continuous layering is analyzed, the expressions derived for the decoding probability regions allow numerical computation of finite level coding upper bounds. Noticing that the gains of two level coding over a MIMO channel are rather small, we consider sub-optimal techniques, which are more straightforward to implement. Among these techniques is the multiple-access channel (MAC) approach with single level coded streams, which is similar in concept to V-BLAST. Closed form expressions for probabilities of decoding regions here are derived, allowing numerical evaluation. We further consider multi-access permutation codes (MAPC). A Hadamard transform is compared with a suggested diagonal permutation code, which are shown to have similar performance, while diagonal permutation has lower implementation complexity. For all approaches, we derive information theoretic upper bounds of achievable rates. [ABSTRACT FROM PUBLISHER]

The sum rate capacity of the multi-antenna broadcast channel has recently been computed. However, the search for efficient practical schemes that achieve it is still ongoing. In this paper, we focus on schemes with linear preprocessing of the transmitted data. We propose two criteria for the preceding matrix design: one maximizing the sum rate and the other maximizing the minimum rate among all users. The latter problem is shown to be quasiconvex and is solved exactly via a bisection method. In addition to preceding, we employ a signal scaling scheme that minimizes the average bit-error-rate (BER). The signal scaling scheme is posed as a convex optimization problem, and thus can be solved exactly via efficient interior-point methods. In terms of the achievable sum rate, the proposed technique significantly outperforms traditional channel inversion methods, while having comparable (in fact, often superior) BER performance [ABSTRACT FROM PUBLISHER]

This paper studies the fundamental transmission limits for ultra wideband (UWB) downlink broadcast channels. The significant contribution of this article is demonstrating the effectiveness of adaptive frequency allocation in UWB systems. We derive an expression for the ergodic sum-rate capacity of an UWB channel with perfect channel knowledge, and show the advantage of an adaptive system that uses channel state information (CSI), over a conventional, non-adaptive system. A capacity achieving system is also proposed. In this system, the transmitter assigns each frequency band to the user that has the best channel gain, and adaptively changes the bandwidth allocation according to the known channel state. The sum-rate capacity can be achieved in a fast fading channel. For a slow fading channel the system must apply fair scheduling to ensure service to all users, and the optimization must be performed for each channel realization. In this case, we also take advantage of the wide bandwidth of the UWB system and show the advantage of an frequency adaptive systems over non frequency adaptive systems [ABSTRACT FROM PUBLISHER]

We consider two-user MIMO broadcast and interference channels in which confidential messages intended for each receiver are kept secret from the other receiver. The confidential secrecy rates are nonconvex functions of transmit covariance matrices, which makes it intractable to find optimal transmit covariance matrices analytically. In the MIMO broadcast channels, we prove the weighted secrecy sum rate maximization has zero duality gap and KKT conditions are necessary conditions for the optimal solution. We apply the block successive lower-bound maximization technique to nonconvex weighted secrecy sum rate maximization problems. We also derive numerical algorithms for MIMO interference channels and Gaussian wiretap channels with a cooperative jammer. Every limit point achieved by the proposed algorithms is a local optimal solution that satisfies the KKT conditions. Numerical results show that the proposed algorithms outperform existing suboptimal algorithms in terms of secrecy rates. [ABSTRACT FROM PUBLISHER]

This paper considers a scenario for multi-user multi-input multi-output (MIMO) communication systems when perfect channel state information at the transmitter (CSIT) is given while the equivalent channel state information at the receiver (CSIR) is not available. Such an assumption is valid for the downlink multi-user MIMO systems with linear precoders that depend on channels to all receivers. We propose a concept called dual systems with zero-forcing design based on the duality principle, originally proposed to relate the Gaussian multi-access channel (MAC) and the Gaussian broadcast channel (BC). For the K-user Nx 2 MIMO BC with N antennas at the transmitter and two antennas at each of the K receivers, we design a downlink interference cancellation (IC) transmission scheme by obtaining the dual of uplink MAC systems employing IC methods. The transmitter simultaneously sends K precoded Alamouti codes, one for each user. Each receiver zero-forces the unintended user's Alamouti codes and decouples its own data streams using two simple linear operations independent of CSIR. Analysis shows that the proposed scheme achieves a diversity gain of 2(N-K+1) for equal energy constellations with short-term power and rate constraints. Power allocation among K users can also be performed to improve the array gain but not the diversity gain. Numerical results demonstrate that the bit error rate of the downlink IC scheme has a diversity gain improvement compared to the block diagonalization (BD) method, which requires global channel information at each node. [ABSTRACT FROM PUBLISHER]

Time-slotted ALOHA packetized multiple-access has been extensively used in satellite communications, and has recently been attracting considerable attention in wireless Ad- hoc networks. In this paper, we consider a time-slotted ALOHA system which combines multiple-access, broadcasting channels and rate splitting. This system allows some transmission bits to be reliably received even when collisions occur and more bits to be reliably received in the absence of collisions. In contrast to previous work, our work focuses on the case in which the transmission channels obey i.i.d (independent and identically distributed) Rayleigh fading. Two fundamental problems are considered. The first one is the calculation of the system capacity, and the second one is how to select an appropriate channel coding scheme with which the system achieves its capacity. We shall review the single time slotted capacity, and present the total capacity expression with the knowledge of channel side information. We will then derive a threshold for the transmission probability in a single time slot provided that all the users have the same transmission probability. It will be shown that when the transmission probability is greater than the derived threshold, low-resolution codes can help the system achieve its capacity. We shall also present an explicit estimation method for computing the threshold, and prove that it can be extended to the more general case when the transmission probabilities are approximately equal. [ABSTRACT FROM PUBLISHER]

This paper focuses on the broadcast channel of an interactive multibeam broadband satellite (MBS) system with a transparent architecture. In particular, a cross-layer design is proposed for the packet scheduling on a forward link that implements adaptive coding and modulation (ACM). A cross-layer approach is considered whereby the physical and medium access control (MAC) layers share knowledge of the channel dynamics in presence of ACM. Transmission power and symbol rate are assumed to be constant, and hence the bit rate is time and space dependant according to the channel conditions. An architecture is proposed which relies on the physical characteristics of the Ka-band satellite propagation channel and the definition of "correlated areas". The stable throughput region has been derived assuming full-queue traffic conditions. Moreover, the proposed architecture is simple but flexible enough to allow the implementation of different scheduling policies like the proportionally fair or opportunistic ones. Finally, a new time-fair policy appropriate for wet seasons is proposed. It has the property of isolating users in clear-sky conditions from the effects of the reduced transmission rate experienced by users under a rain fade [ABSTRACT FROM PUBLISHER]

In this paper, we study the linear transmission (or beamforming) techniques in MIMO broadcast channels (BC) and propose beamforming algorithms for rate optimization. Our method for algorithm design draws on ideas from the classic Arimoto-Blahut algorithm. Like Arimoto-Blahut algorithm, our algorithms operate iteratively in a two-stage manner, i.e., in one iteration, the first stage is for updating test conditional probabilities, the second for updating beamforming matrices, and both stages are composed of simple convex subproblems. Optimal transmit beamforming for weighted sum rate maximization, weighted rate balancing, and proportional fair rate allocation in MIMO BC are considered. We rediscover the weighted sum-rate beamforming weighted minimum mean square error (WSRBF-WMMSE) algorithm in [1] for MIMO BC. And we apply our method together with uplink-downlink duality to optimal beamforming for weighted rate balancing and proportional fair rate allocation in MIMO BC. We show experimentally that our algorithm for rate balancing requires less computation time to converge than existing algorithms without performance loss, and the algorithm for proportional fair rate allocation can achieve the balance between sum rate maximization and minimum rate maximization. [ABSTRACT FROM PUBLISHER]

We consider a single-antenna broadcast block fading channel with n users where the transmission is packet- based. We define the (packet) delay as the minimum number of channel uses that guarantees all n users successfully receive m packets. This is a more stringent notion of delay than average delay and is the worst case (access) delay among the users. A delay optimal scheduling scheme, such as round-robin, achieves the delay of mn. For the opportunistic scheduling (which is throughput optimal) where the transmitter sends the packet to the user with the best channel conditions at each channel use, we derive the mean and variance of the delay for any m and n. For large n and in a homogeneous network, it is proved that the expected delay in receiving one packet by all the receivers scales as nlogn, as opposed to n for the round-robin scheduling. We also show that when m grows faster than (log n)r, for some r > 1, then the delay scales as mn. This roughly determines the time- scale required for the system to behave fairly in a homogeneous network. We then propose a scheme to significantly reduce the delay at the expense of a small throughput hit. We further look into the advantage of multiple transmit antennas on the delay. For a system with M antennas in the transmitter where at each channel use packets are sent to M different users, we obtain the expected delay in receiving one packet by all the users. [ABSTRACT FROM PUBLISHER]

We consider broadcasting to multiple destinations with uneven quality receivers. Based on their quality of reception, we group destinations in tiers and transmit using hierarchical modulations. These modulations are known to offer a practical means of achieving variable error protection of the broadcasted information to receivers of variable quality. After the initial broadcasting step, tiers successively re-broadcast part of the information they received from tiers of higher-quality to tiers with lower reception capabilities. This multi-tier cooperative broadcasting strategy can accommodate variable rate and error performance for different tiers but requires complex demodulation steps. To cope with this complexity in demodulation, we derive simplified per-tier detection schemes with performance close to maximum-likelihood and ability to collect the diversity provided as symbols propagate through diversified channels across successive broadcastings. Error performance is analyzed and compared to (non)-cooperative broadcasting strategies. Simulations corroborate our theoretical findings. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the transmission completion time minimization problem in an additive white Gaussian noise (AWGN) broadcast channel, where the transmitter is able to harvest energy from the nature, using a rechargeable battery. The harvested energy is modeled to arrive at the transmitter during the course of transmissions. The transmitter has a fixed number of packets to be delivered to each receiver. The objective is to minimize the time by which all of the packets are delivered to their respective destinations. To this end, we optimize the transmit powers and transmission rates in a deterministic setting. We first analyze the structural properties of the optimal transmission policy in a two-user broadcast channel via the dual problem of maximizing the departure region by a fixed time T. We prove that the optimal total transmit power sequence has the same structure as the optimal single-user transmit power sequence in . In addition, the total power is split optimally based on a cut-off power level; if the total transmit power is lower than this cut-off level, all transmit power is allocated to the stronger user; otherwise, all transmit power above this level is allocated to the weaker user. We then extend our analysis to an M-user broadcast channel. We show that the optimal total power sequence has the same structure as the two-user case and optimally splitting the total power among M users involves M-1 cut-off power levels. Using this structure, we propose an algorithm that finds the globally optimal policy. Our algorithm is based on reducing the broadcast channel problem to a single-user problem as much as possible. Finally, we illustrate the optimal policy and compare its performance with several suboptimal policies under different settings. [ABSTRACT FROM PUBLISHER]

We propose joint user-and-hop scheduling over dual-hop block-fading broadcast channels in order to exploit multi-user diversity gains and multi-hop diversity gains all together. To achieve this objective, the first and second hops are scheduled opportunistically based on the channel state information. The joint scheduling problem is formulated as maximizing the weighted sum of the long term achievable rates of the users under a stability constraint, which means that in the long term the rate received by the relay should equal the rate transmitted by it, in addition to power constraints. We show that this problem is equivalent to a single-hop broadcast channel by treating the source as a virtual user with an optimal weight that maintains the stability constraint. We show how to obtain the source weight either off-line based on channel statistics or on real-time based on channel measurements. Furthermore, we consider special cases including the maximum sum-rate scheduler and the proportional fair scheduler. We also show how to extend the scheme into one that allows multiple user scheduling via superposition coding with successive decoding. Numerical results demonstrate that our proposed joint scheduling scheme enlarges the rate region as compared to scheduling schemes that exploit the diversity gains partially. [ABSTRACT FROM PUBLISHER]

We develop a realistic model for multiple-input multiple-output (MIMO) broadcast channels, where each randomly located user's average SNR depends on its distance from the transmitter. With perfect channel state information at the transmitter (CSIT), the average sum capacity is proven to scale for many users like \fracα, M2 log K instead of M log log K, where α, M, and K denote the path loss exponent, the number of transmit antennas, and the number of users in a cell. With only partial CSIT, the sum capacity at high SNR eventually saturates due to interference, and the saturation value scales for large B like \fracM BM-1, where B denotes the quantization resolution for channel feedback. [ABSTRACT FROM PUBLISHER]

We study information-rate calculations and coded cooperation strategies for relay channels with frequency-selective (FS) fading. We develop suitable channel trellises for the multiaccess and broadcast parts of the relay channel, and employ simulation-based techniques to calculate (approximate) ergodic information-rate bounds with FS Rayleigh fading. Our results show that frequency selectivity provides higher information rates than flat fading when the fading coefficients are known at the receiver, however, the improvement becomes marginal with increasing number of channel taps (when the overall signal to noise ratio is kept constant). Furthermore, we develop a distributed turbo-coding strategy and several decode-and-forward type detection/decoding schemes to ensure successful cooperative communication where the source and the relay may transmit simultaneously. We show that with suitable coding and iterative decoding, one can approach the approximate information-rate limits closely, and that detection schemes based on MMSE criterion provide a good performance/complexity trade-off. [ABSTRACT FROM PUBLISHER]

In a single-input single-output (SISO) downlink with multiple users, to obtain the multiuser diversity gain, the full channel state information (CSI) of all users is required for selecting the desired user and transmission mode. However, feedback channels are often capable of carrying only a limited number of bits. With such rate limited feedback links, we intend to maximize the average throughput of each user by designing transmit power levels, signal constellations and feedback thresholds jointly. Both un-coded adaptive M-ary quadrature amplitude modulation (MQAM) and adaptive trellis-coded modulation (TCM) are investigated. A nested iterative algorithm is proposed to obtain a finite number of transmission modes and thresholds. Optimization in the heterogeneous network is also considered. Simulation results demonstrate a small number of feedback bits make the throughput approach to that with perfect CSI. As the number of users increases, the multiuser diversity gain is achieved and the average feedback load of each user is reduced. [ABSTRACT FROM PUBLISHER]

In CDMA2000 1xEV-DO broadcast and multicast services (BCMCS), Reed-Solomon (RS) coding is applied to the layers above the turbo code, which is effective in correcting long bursts of errors when an additional block interleaving mechanism is used to increase the time diversity. This is controlled by changing the width of the error control block (ECB), which converts error bursts into random patterns. We propose and evaluate an energy model of the RS decoding process under varying conditions of Rayleigh fading on the broadcast channel, with different levels of block interleaving within those permitted by the BCMCS specification. Simulation results show that our model accurately predicts the energy consumption of the RS decoding process, and is thus able to contribute to the development of energy-efficient broadcast services. [ABSTRACT FROM PUBLISHER]

In cdma2000 1xEV-DO Broadcast and Multicast Services (BCMCS), Reed-Solomon coding is applied to the layers above the turbo code, and is particularly effective in correcting long bursts of errors. An additional block interleaving mechanism improves the performance of RS coding by increasing the time diversity, to an extent controlled by the width of the error control block (ECB), which converts error bursts into random patterns. We propose and evaluate a performance model of RS coding under varying conditions of Rayleigh fading on the broadcast channel, within the levels of block interleaving that the BCMCS specification allows. Simulation results show that our model predicts the performance of RS coding accurately. This evaluation will allow a service provider to determine the most efficient RS code for their target service quality, that maximizes the effective data-rate and minimizes the energy required for the RS decoding process. [ABSTRACT FROM PUBLISHER]

A multiple antenna downlink channel where limited channel feedback is available to the transmitter is considered. In a vector downlink channel (single antenna at each receiver), the transmit antenna array can be used to transmit separate data streams to multiple receivers only if the transmitter has very accurate channel knowledge, i.e., if there is high-rate channel feedback from each receiver. In this work it is shown that channel feedback requirements can be significantly reduced if each receiver has a small number of antennas and appropriately combines its antenna outputs. A combining method that minimizes channel quantization error at each receiver, and thereby minimizes multi-user interference, is proposed and analyzed. This technique is shown to outperform traditional techniques such as maximum-ratio combining because minimization of interference power is more critical than maximization of signal power in the multiple antenna downlink. Analysis is provided to quantify the feedback savings, and the technique is seen to work well with user selection and is also robust to receiver estimation error. [ABSTRACT FROM PUBLISHER]

A user-identity feedback method is proposed to achieve multi-user diversity in broadcast channels. This method associates the feedback slots with pre-determined thresholds that diminish with time, and allows feedback from those users whose channel states exceed the threshold assigned to the current slot. Since the threshold can approximate the channel state, this method requires only user-identity feedback. In Rayleigh fading channels, this method is mathematically shown to achieve the sum-rate capacity asymptotically with a large number of users, while requiring only a few feedback slots and little transmission power. [ABSTRACT FROM PUBLISHER]

Cooperative broadcast aims to deliver common messages to all receiver nodes in the wireless network by utilizing cooperation between them. This can have many important applications like broadcasting control messages and cellular phone- based teleconference/games among a group of people. In this work, we investigate the cooperative broadcast from the diversity-multiplexing-delay (D-M-D) tradeoff point of view, which has become a popular tool in analyzing MIMO and cooperative protocols. The major contribution is that we derive the optimal D-M-D tradeoff curves for arbitrary number of receive nodes and arbitrary maximum number of automatic retransmission request (ARQ) rounds. Interestingly, it is shown that the achievable diversity gain is always restricted by two special situations. We compare our results with previous results on the achievable diversity-multiplexing (D-M) tradeoff of cooperative broadcast channels where no feedback is taken into consideration to show the significant diversity benefit of ARQ transmission. [ABSTRACT FROM PUBLISHER]

We discuss new space-time codes tailored to point-to-multipoint, or broadcast, communications using layered source coding. Our codes can be encoded (and decoded) differentially, and they are based entirely on phase-shift keying. We discuss design criteria for the codes, and the design of optimal and suboptimal receiver structures. We also discuss the relation between our codes and a differentially encoded Alamouti code. Finally, we illustrate how our codes can be used to improve the throughput of a broadcasting network. [ABSTRACT FROM PUBLISHER]

We consider the minimization of the transmission completion time with a battery limited energy harvesting transmitter in an M-user AWGN broadcast channel where the transmitter is able to harvest energy from the nature, using a finite storage capacity rechargeable battery. The harvested energy is modeled to arrive (be harvested) at the transmitter during the course of transmissions at arbitrary time instants. The transmitter has fixed number of packets for each receiver. Due to the finite battery capacity, energy may overflow without being utilized for data transmission. We derive the optimal offline transmission policy that minimizes the time by which all of the data packets are delivered to their respective destinations. We analyze the structural properties of the optimal transmission policy using a dual problem. We find the optimal total transmit power sequence by a directional water-filling algorithm. We prove that there exist M-1 cut-off power levels such that user i is allocated the power between the i-1st and the ith cut-off power levels subject to the availability of the allocated total power level. Based on these properties, we propose an algorithm that gives the globally optimal offline policy. The proposed algorithm uses directional water-filling repetitively. Finally, we illustrate the optimal policy and compare its performance with several suboptimal policies under different settings. [ABSTRACT FROM PUBLISHER]

We consider relay broadcast channels (RBCs) with multiple antennas at all nodes. A practical linear precoding, relaying and combining scheme is proposed. Under an overall power constraint, we derive the optimal power allocation solution in a closed form. A low complexity beamforming vector optimization algorithm is proposed to maximize the effective channel gains and improve the system performance. Simulation results are presented for various channel configurations, which show that the proposed cooperative beamforming algorithm achieves performance very close to that of the exhaustive search algorithm but with a much lower complexity, and the maximum diversity gain is always attained. [ABSTRACT FROM PUBLISHER]