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As functionality of vehicles increases in complexity, the demand on the in-vehicle networks increases as well. Maximum bus utilization often becomes the communication bottleneck. One way to satisfy the high bandwidth requirement for future vehicles is to use a higher bandwidth bus or multiple buses. However, the use of a higher bandwidth bus increases the cost of the network. Similarly, the use of multiple buses increases the cost as well as the complexity of wiring and network handling. Both options are becoming solutions to high bandwidth demand. An alternative option is the development of a higher layer protocol that uses data-reduction (DR) techniques to reduce the amount of data to be transferred. Its goal is to communicate the same amount of information using less bus bandwidth. It would be acceptable, provided that it does not increase the message latencies significantly so that the safety of the vehicle is not compromised. The cost of the protocol is expected to be marginal because it consists of one-time changes to software. Various DR algorithms are available in the literature, but DR technology has not been introduced in in-vehicle protocol standards. This paper presents a unique DR methodology, along with its comparison with other proposed methodologies. The performance of this new DR algorithm is found to be better than that of the existing DR algorithms for a wide range of signal dynamics. The cost, as well as the impact of this protocol on the end-to-end message latency, has been found to be very marginal. Index Terms--Controller area network (CAN), data reduction (DR), event-triggered bus, in-vehicle network, multiplexing.

The opportunistic beamforming system (OBS) is currently receiving much attention in the field of downlink beamforming due to its simple random beamforming, low feedback complexity, and same throughput scaling obtained with perfect channel-state information using dirty paper coding at the transmitter. In this paper, we focus on its closed-form throughput evaluation over Rayleigh fading channels, based on the asymptotic theory of extreme order statistics. First, the throughput of a single-beam OBS is investigated, and an analytical solution tighter than the previously reported one is derived. Then, the asymptotic throughput bounds on a multibeam OBS are presented, and also, our analytical expression is shown to be very tight with the simulation results even with fewer users. After that, we argue that the reported conclusion that the single-beam OBS is much preferable to the multibeam OBS in the high-signal-to-noise-ratio (SNR) regime is inaccurate, but that, instead, it is satisfied only when the number of users is very small, due to its limited multiuser diversity gain. Finally, we show that four transmit beams is the most preferable in the multibeam OBS with a large number of users and moderate SNR, which arrives at the tradeoff between increasing spatial multiplexing gain and disappearing multiuser diversity gain. Index Terms--Multiple-input single-output (MISO), multiuser diversity, opportunistic beamforming system (OBS), spatial multiplexing, throughput.

In this paper, we propose a novel distributed interleaved random space-time code (IR-STC) designed for multisource cooperation (MSC) employing various relaying techniques, namely, amplify-forward, decode-forward, soft decode-forward, and differential decode-forward. We introduce a two-phase communication regime for our IR-STC-aided MSC and propose a novel structured embedded (SE) random interleaver-generation method. We also characterize the achievable performance of our proposed IR-STC design in conjunction with various relaying techniques communicating over different intersource Nakagami-m fading channels. Index Terms--Cooperative communications, interleaver division multiplexing, relaying, space-time coding.

Tilt error can affect a serious effect to holographic data storage system using angle(polytopic) multiplexing. Because the tolerance about tilt error is very tight it is important to measure the tilt error and compensate it. In this paper, tilt error measurement system with additional red laser and reflection geometry is suggested and servo control experiments are conducted. A servo controller to compensate tilt error is designed using disturbance observer. Amount of tilt is decreased smaller than 0.01 degree and signal-to-noise ratio is increased with the tilt servo controller when 0.216 degree of tilt disturbance is applied. Index Terms--Holographic memories, servosystems.

Generally limited feedback systems that multiplex multiple user signals are noise power limited in the low signal-to-noise-ratio (SNR) regime and interference power limited in the high SNR regime. If the amount of feedback does not grow with SNR, then there is a sum rate ceiling that increasing the transmit power alone cannot surpass. This paper proposes a simple dual mode system where the base station serves either one user or as many users as the number of transmit antennas. The switching mechanism is smooth and is based on instantaneous system conditions. The mobile determines its preferred transmission mode by using a very simple signal-to-interference-and-noise-ratio (SINR) threshold. Based on the mobiles' feedback, the base station chooses the method of signalling accordingly. With a finite number of feedback bits per mobile, it is shown that the proposed system achieves close to the maximum of the sum-rate for single user and multiuser modes. We identify the preferrable mode for an asymptotically large number of users and/or SNR. This proposed architecture is suitable for systems with moderate coherence time, a moderate to large number of users, and a moderate SNR that cannot afford complex processing at the base station or at the mobile. Index Terms--Gaussian broadcast system, dual mode multiuser system, sum-rate ceiling.

This paper addresses the performance of bit-interleaved coded multiple beamforming (BICMB) [1], [2] with imperfect knowledge of beamforming vectors. Most studies for limited-rate channel state information at the transmitter (CSIT) assume that the precoding matrix has an invariance property under an arbitrary unitary transform. In BICMB, this property does not hold. On the other hand, the optimum precoder and detector for BICMB are invariant under a diagonal unitary transform. In order to design a limited-rate CSIT system for BICMB, we propose a new distortion measure optimum under this invariance. Based on this new distortion measure, we introduce a new set of centroids and employ the generalized Lloyd algorithm for codebook design. We provide simulation results demonstrating the performance improvement achieved with the proposed distortion measure and the codebook design for various receivers with linear detectors. We show that although these receivers have the same performance for perfect CSIT, their performance varies under imperfect CSIT. Index Terms--Beamforming, Bit-interleaved coded modulation, diversity, spatial multiplexing, limited feedback, BICMB.

This paper investigates the application of Zipper orthogonal frequency-division multiplexing (OFDM), which is a frequency-domain duplexing technique based on interleaving subcarriers, to multiple-antenna cellular communications. By studying the Cramer-Rao lower bound as well as the performance of a minimum-mean-square-error-based interpolator, we show that the interleaved subcarriers make it possible for the base station to obtain accurate instantaneous downlink channel state information (CSI) from uplink channel measurements. However, the interleaved uplink and downlink subcarriers could introduce interference leakage when the intersubcarrier orthogonality is destroyed in multiple-cell environments. We address this issue by analyzing the uplink-to-downlink power leakage and show that with proper system configuration, such interference only has a marginal effect in typical land mobile radio environments. Finally, by considering maximum ratio transmission as an example, we demonstrate the benefit of knowing instantaneous downlink CSI in multiple-antenna Zipper OFDM systems. Index Terms--Cellular communication, instantaneous channel state information (CSI), interleaved frequency-domain duplexing (FDD), maximum ratio transmission (MRT).

In a time-division duplexing (TDD)/code-division multiple-access (CDMA) cellular network with asymmetric data traffic, dynamic channel allocation (DCA) enhances resource utilization compared with fixed channel allocation (FCA). However, it also induces base-to-base and mobile-to-mobile crossed-slot intercell interference, which can severely degrade system performance. To deal with this problem, a decentralized scheme is proposed, which combines an interference-aware DCA algorithm with space-time linear minimum-mean-square-error (LMMSE) joint detection at the base and mobile stations. The former assigns active links to timeslots in a way that crossed-slot interference is mitigated, while the latter suppresses the remaining intercell interference (along with intersymbol and intracell interference), exploiting its spatio-temporal autocorrelation statistics. The performance of this scheme is evaluated in terms of downlink and uplink signal-to-interference-plus-noise ratio (SINR) outage and average throughput via analytical approximations and Monte Carlo simulations, and it is compared with that of benchmark random DCA (RDCA) and FCA schemes. The cases of single- and dual-antenna reception with perfect and imperfect channel state information are examined. It is shown that the proposed scheme achieves higher average throughput than FCA (particularly for dual-antenna reception) as well as RDCA (for heavy traffic loads). These throughput gains are more significant in uplink than in downlink. Index Terms--Antenna arrays, code-division multiple access (CDMA), land mobile radio cellular systems, resource management, signal detection, time-division duplexing (TDD).

In this paper, we compare the performance of two downlink capacity-improvement schemes based on orthogonal code-hopping multiplexing (OCHM) and multiple scrambling codes (MSCs). Both OCHM and MSC systems have been proposed to overcome a code-limitation problem in a code division multiple access (CDMA) downlink. We mathematically analyze the user capacity in a general form, considering various factors such as user activity, spreading factor, amount of transmission symbol energy that is allocated to common control channels, amount of outer-cell interference, orthogonality factor, and sectorization factor. Numerical examples show that the capacity gain of the OCHM-based system increases as the other-cell interference decreases and the channel activity decreases. Thus, the OCHM-based system is a more effective scheme than the MSC-based system, considering that a code-limited situation more frequently occurs in the case of low other-cell interference and low channel activity. However, the OCHM-based system is more sensitive to the orthogonality factor. Index Terms--Downlink power allocation, multiple scrambling codes (MSCs), orthogonal code hopping multiplexing (OCHM), user capacity.

On the multiantenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, which is known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions such as Tomlinson-Harashima precoding are sensitive to channel state information (CSI) inaccuracy. This paper considers a more practical design called per user unitary and rate control (PU2RC), which has been proposed for emerging cellular standards. PU2RC supports multiuser simultaneous transmission, enables limited feedback, and is capable of exploiting multiuser diversity. Its key feature is an orthogonal beamforming (or precoding) constraint, where each user selects a beamformer (or precoder) from a codebook of multiple orthonormal bases. In this paper, the asymptotic throughput scaling laws for PU2RC with a large user pool are derived for different regimes of the signal-to-noise ratio (SNR). In the multiuser interference-limited regime, the throughput of PU2RC is shown to logarithmically scale with the number of users. In the normal SNR and noise-limited regimes, the throughput is found to scale double logarithmically with the number of users and linearly with the number of antennas at the base station. In addition, numerical results show that PU2RC achieves higher throughput and is more robust against CSI quantization errors than the popular alternative of zero-forcing beamforming if the number of users is sufficiently large. Index Terms--Broadcast channels, feedback communication, multiuser channels, space division multiplexing.

This paper presents a novel generalized transceiver architecture, i.e., Multicarrier Interleave-Division-Multiplexing. aided Interleave Division Multiple Access (MC-IDM-IDMA). A parallel interference cancellation (PIC)-aided iterative multiuser detection (MUD) algorithm, is introduced, and the convergence behavior of the system is evaluated with the aid of EXtrinsic Information Transfer (EXIT) charts under the assumption of an equal-power multiuser scenario. Three interesting design tradeoffs of the MC-IDM-IDMA system are analyzed: 1) the multiplexing versus diversity tradeoffs; 2) the coding versus spreading tradeoffs, where the achievable bandwidth efficiency of both MC-IDM and MC-IDMA are characterized, and a general design rule is provided for low-rate codes; and 3) the complexity versus performance tradeoffs and the EXIT characteristics of two different MUD algorithms are investigated, leading to a reduced-complexity hybrid MUD. Index Terms--EXtrinsic Information Transfer (EXIT) charts, interleave division multiplexing/interleave division multiple access (IDM/IDMA), multicarrier (MC), multiuser detection (MUD).

Aggressive technology scaling raises the need for efficient methods to characterize and model circuit variation at both the front and back end of line, where critical parameters such as threshold voltage and parasitic capacitance must be carefully modeled for accurate circuit performance. In this paper we address this need by contributing a test circuit methodology for the extraction of spatial, layout and size dependent variations at both device and interconnect levels. The test chip uses a scan chain approach combined with low-leakage and low-variation switches, and Kelvin sensing connections, providing access to detailed analog device characteristics in large arrays of test devices. Variation measurement using the designed test chip has proven successful for both device and interconnect test structures. The parameter extraction and variation analyses made possible by the variation test chip enable the identification of likely variation sources, quantification of circuit impact and sensitivity, and specification of layout practices for variation minimization. Index Terms--Design for manufacturability, statistical metrology, statistical modeling, variation.

Space--time codes built out of Alamouti components have been adopted in wireless standards such as UMTS, IEEE 802.11n, and IEEE 802.16, where they facilitate higher data rates through multiplexing of parallel data streams and the addition of two or more antennas at the receiver that perform interference cancellation. This correspondence provides new theoretical insight into different algorithms for interference cancellation through a Bayesian analysis that expresses performance as a function of signal-to-noise ratio (SNR) in terms of the "angles" between different space-time coded data streams. Index Terms--Alamouti code, Bayesian analysis, decoding algorithms, interference cancellation, Quaternion arithmetic, space-time block codes.

The problem of resource allocation to maximize the outage exponent over a fading relay channel using the decode-and-forward protocol with quantized channel state feedback (CSF) is studied. Three different scenarios are considered: relay-to-source, destination-to-relay, and destination-to-source-and-relay CSF. In the relay-to-source CSF scenario, it is found that using merely one bit of CSF to control the source transmit power is sufficient to achieve the multiantenna upper bound in a range of multiplexing gains. In the destination-to-relay CSF scenario, the systems slightly outperform dynamic decode-and-forward (DDF) at high multiplexing gains, even with only one bit of feedback. Finally, in the destination-to-source-and-relay CSF scenario, if the source-relay channel gain is unknown to the feedback quantizer at the destination, the diversity gain only grows linearly in the number of feedback levels, in sharp contrast to an exponential growth for multiantenna channels. In this last scenario, a simple scheme is shown to perform close to the corresponding upper bound. Index Terms--Cooperative communications, diversity methods, diversity-multiplexing tradeoff, fading channels, large-deviation analysis, power control, relay channels.

Binary coding of multiplexed signals and images has been studied in the context of spectroscopy with models of either purely constant or purely proportional noise, and has been shown to result in improved noise performance under certain conditions. We consider the case of mixed noise in an imaging system consisting of multiple individually-controllable sources (X-ray or near-infrared, for example) shining on a single detector. We develop a mathematical model for the noise in such a system and show that the noise is dependent on the properties of the binary coding matrix and on the average number of sources used for each code. Each binary matrix has a characteristic linear relationship between the ratio of proportional-to-constant noise and the noise level in the decoded image. We introduce a criterion for noise level, which is minimized via a genetic algorithm search. The search procedure results in the discovery of matrices that outperform the Hadamard S-matrices at certain levels of mixed noise. Simulation of a seven-source radiography system demonstrates that the noise model predicts trends and rank order of performance in regions of nonuniform images and in a simple tomosynthesis reconstruction. We conclude that the model developed provides a simple framework for analysis, discovery, and optimization of binary coding patterns used in multiplexed imaging systems. Index Terms--Binary coding, Hadamard spectroscopy, mixed noise, multiplexing.

This paper presents a novel Call Admission Control (CAC) algorithm based on the statistical multiplexing of VBR traffic. The proposed algorithm is called Statistical Multiplexing based on Discrete Bandwidth levels of GOP rate (SMDB) because the solution is based on the discretization of the GOP rate in a set of bandwidth levels and on the time characteristics of discrete bandwidth levels of MPEG sources. SMDB is compared with another statistical CAC based on the Normal/Lognormal distribution of the GOP rate (SMND). SMDB outperforms SMND in many situations such as high variance around the average video traffic GOP rate of sources and heavy traffic load. The new CAC has been tested in the new generation satellite platform called Digital Video Broadcasting via Return Channel Satellite (DVB-RCS). A high system utilization and multiplexing gain with respect to QoS constraints is obtained. Index Terms--Call admission control, DVB-RCS, MPEG traffic sources, statistical multiplexing.

In this paper, a local optimization framework is proposed, which is able to include system constraints including channel availability, receiver availability and tuning overhead by linear mathematical formulations so that it is sufficient to obtain the optimal performance in terms of message delay. A mixed integer linear programming (MILP) based scheme for passive star coupled WDM optical networks is presented. Based on the new solution, the wavelength assignment and message sequence that guarantee the delivery of the given traffic request, while minimizing the average delay can be achieved. Moreover, the negative effect of the tuning overhead has been incorporated into the new algorithm, which has been ignored in most of the previous work. Numerical results obtained suggest that the proposed scheme is a promising approach for optimizing the network performance in terms of average message delay. Index Terms--Optical fiber networks, packet switching, wavelength division multiplexing, scheduling.

Constructions of multiblock space-time coding schemes that are optimal with respect to diversity-multiplexing (D-M) tradeoff when coding is applied over any number of fading blocks are presented in this correspondence. The constructions are based on a left-regular representation of elements in some cyclic division algebra. In particular, the main construction applies to the case when the quasi-static fading interval equals the number of transmit antennas, hence the resulting scheme is termed a minimal delay multiblock space-time coding scheme. Constructions corresponding to the cases of nonminimal delay are also provided. As the number of coded blocks approaches infinity, coding schemes derived from the proposed constructions can be used to provide a reliable multiple-input multiple-output (MIMO) communication with vanishing error probability. Index Terms--Cyclic-division algebras, diversity-multiplexing (D-M) tradeoff, fading channels, multiblock space-time codes, multiple-input multiple-output (MIMO) channels, number fields, space-time codes.

This correspondence demonstrates the significant gains that multiple-access users can achieve from sharing a single amplify--forward relay in slow-fading environments. The proposed protocol, namely, multiple-access amplify-forward (MAF), allows for a low-complexity relay and achieves the optimal diversity--multiplexing tradeoff (DMT) at high multiplexing gains. Analysis of the protocol further reveals that it outperforms both the compress-forward strategy at low multiplexing gains and the dynamic decode-forward protocol at high multiplexing gains. An interesting feature of the proposed protocol is that, at high multiplexing gains, it resembles a multiple-input single-output (MISO) system, and at low multiplexing gains, it provides each user with the same DMT as if there were no contention for the relay from the other users. Index Terms--Amplify-forward, block-fading channel, cooperative diversity, diversity--multiplexing tradeoff (DMT), multiple-access relay channel (MARK), wireless networks.

For the fully connected K user wireless interference channel where the channel coefficients are time-varying and are drawn from a continuous distribution, the sum capacity is characterized as C(SNR) = K/2 log(SNR) + o(log(SNR)). Thus, the K user time-varying interference channel almost surely has K/2 degrees of freedom. Achievability is based on the idea of interference alignment. Examples are also provided of fully connected K user interference channels with constant (not time-varying) coefficients where the capacity is exactly achieved by interference alignment at all SNR values. Index Terms--Capacity, degrees of freedom, interference alignment, interference channel, multiple-input-multiple-output (MIMO), multiplexing.

Space division multiplexing (SDM)/orthogonal frequency division multiplexing (OFDM) systems transmit different data using the same frequency, so it is necessary to separate the simultaneously received signals in the receiver. Previous studies have shown that maximum likelihood detection (MLD) provides the best bit error rate (BER) performance. However, the complexity of MLD exponentially increases with the constellation size and the number of transmit antenna branches. Therefore, it is impractical to use a full MLD without reducing its computational complexity, because it would be prohibitively large for implementation. Recently, the use of QR decomposition with an M-algorithm (QRD-M) has been proposed to reduce the system complexity while maintaining the performance of the system. However, the QRD-M performance depends on the number of surviving symbol replica candidates. When QRD-M is used with a small number of surviving symbol replica candidates, the performance declines, but when there is a large number of surviving symbol replica candidates and the transmitter antenna branches, QRD-M requires a large memory to maintain their branch metrics, and a long latency time is also required. To reduce these problems, in this paper, we propose a parallel detection algorithm using multiple QR decompositions with permuted channel matrices for SDM/OFDM systems. Index Terms--M-algorithm, maximum likelihood detection (MLD), multiple-input multiple-output (MIMO), orthogonal frequency division multiplexing (OFDM), QR decomposition, QR decomposition with an M-algorithm (QRD-M), space division multiplexing (SDM).

Multipinhole single photon emission computed tomography (SPECT) imaging has several advantages over single pinhole SPECT imaging, including an increased sensitivity and an improved sampling. However, the quest for a good design is challenging, due to the large number of design parameters. The effect of one of these, the amount of overlap in the projection images, on the reconstruction image quality, is examined in this paper. The evaluation of the quality is based on efficient approximations for the linearized local impulse response and the covariance in a voxel, and on the bias of the reconstruction of the noiseless projection data. Two methods are proposed that remove the overlap in the projection image by blocking certain projection rays with the use of extra shielding between the pinhole plate and the detector. Also two measures to quantify the amount of overlap are suggested. First, the approximate method, predicting the contrast-to-noise ratio (CNR), is validated using postsmoothed maximum likelihood expectation maximization (MLEM) reconstructions with an imposed target resolution. Second, designs with different amounts of overlap are evaluated to study the effect of multiplexing. In addition, the CNR of each pinhole design is also compared with that of the same design where overlap is removed. Third, the results are interpreted with the overlap quantification measures. Fourth, the two proposed overlap removal methods are compared. From the results we can conclude that, once the complete detector area has been used, the extra sensitivity due to multiplexing is only able to compensate for the loss of information, not to improve the CNR. Removing the overlap, however, improves the CNR. The gain is most prominent in the central field of view, though often at the cost of the CNR of some voxels at the edges, since after overlap removal very little information is left for their reconstruction. The reconstruction images provide insight in the multiplexing and truncation artifacts. Index Terms--Multipinhole single photon emission computed tomography (SPECT), multiplexing, overlap, reconstruction image quality.

Following the seminal work of Zheng and Tse, this paper investigates the fundamental diversity and multiplexing tradeoff of multiple-input-multiple-output (MIMO) systems in which knowledge of the channel state at both sides of the link is employed to transmit independent data streams through the channel eigenmodes. First, the fundamental diversity and multiplexing tradeoff of each of the individual substreams is obtained and this result is then used to derive a tradeoff optimal scheme for rate allocation along channel eigenmodes. The tradeoff of spatial multiplexing is finally compared to the fundamental tradeoff of the MIMO channel and to the one of both space only codes and V-BLAST which do not require channel state information (CSI) at the transmit side. Index Terms--Capacity-achieving waterfilling, diversity and multiplexing tradeoff, linear multiple-input multiple-output (MIMO) transceivers, spatial multiplexing systems, Wishart matrices.

We consider the problem of joint source-channel coding for transmitting K samples of a complex Gaussian source over T = bK uses of a block-fading multiple-input multiple-output (MIMO) channel with M transmit and N receive antennas. We consider the case when we are allowed to code over L blocks. The channel gain is assumed to be constant over a block and channel gains for different blocks are assumed to be independent. The performance measure of interest is the rate of decay of the expected mean-squared error with the signal-to-noise ratio (SNR), called the distortion SNR exponent. We first show that using a broadcast strategy similar to that of Gunduz and Erkip, but with a different power and rate allocation policy, the optimal distortion SNR exponent can be achieved for 0 [less than or equal to] b < ([absolute value of N - M] + 1)/min (M, N) and for b > MN[L.sup.2]. This is the first time the optimal exponent is characterized for 1/min(M, N) < b < ([absolute value of N - M] + 1)/min (M, N). Then, we propose a digital layered transmission scheme that uses both time layering and superposition. The new scheme is at least as good as currently known schemes for the entire range of bandwidth expansion factors b, whereas at least for some M, N, and b, it is strictly better than the currently known schemes. Index Terms--Broadcast, distortion signal-to-noise ratio (SNR) exponent, diversity-multiplexing tradeoff, joint source-channel coding, layered source-channel coding, multiple-input multiple-output (MIMO), successive refinement, superposition.

In this paper, for spatial multiplexing with limited feedback, a quantized principal component selection (QPCS) precoding scheme is proposed that achieves comparable capacity to the closed-loop multiple-input multiple-output (MIMO) and furthermore adapts to various fading channel conditions without any additional feedback bits and transmit channel state information (CSI). We propose a systematic design method for a codebook consisting of a finite number of unitary matrices based on a maximizing minimum distance criterion in the one-dimensional angular domain and show that the method outperforms the Grassmannian subspace packing method in various fading channel conditions. The proposed QPCS precoding scheme allows for adjustment of the precoding matrix based on limited feedback information on the principal vectors approximating a MIMO channel in the angular domain according to various channel conditions. Furthermore, for practical implementation of the QPCS precoding scheme, we propose a structured precoder optimization procedure and show that the proposed procedure induces a negligible capacity loss compared with the exhaustive precoder optimization, even with considerably reduced complexity. Index Terms--MIMO systems, spatial multiplexing, linear precoding, limited feedback, antenna array processing.

In this paper, we investigate the effect of spatial correlation on throughput performance of downlink multiantenna transmission schemes exploiting multiuser diversity, in which partial channel information such as signal-to-interference plus noise power ratio (SINR) is available at the transmitter. The asymptotic analysis is performed based on the extreme value theory. From this analysis, we demonstrate that the throughput optimal transmission scheme depends on the degree of the antenna correlation and the operating SNR. Especially, the multiuser spatial multiplexing known as the asymptotically optimal transmission scheme is no longer optimal in highly correlated multiple antenna channels. Index Terms--Multiuser diversity, MIMO, antenna correlation.

In this brief, a high-speed space-division multiplexing (SDM) multiple-input--multiple output (MIMO) decoder using efficient candidate searching is proposed by exploiting the characteristics of QR decomposition and sphere decoder for high throughput rate and low hardware-complexity. A process of efficient candidate searching by shifting the center of constellation with scalable radius reduces the processing time and improves the operational frequency. The proposed architecture can operate at a 166-MHz clock frequency, and the core area is smaller than results from using the K-best SD algorithm since large memory is not required to store extreme candidate paths. In our implementation, the core area is 0.675 m[m.sup.2] using TSMC 90-nm technology. The average throughput of the proposed SDM-MIMO decoder is 95 Mbps with 64-QAM modulation at 30-dB signal-to-noise ratio. Index Terms--Digital communication, maximum-likelihood (ML) detection, space-division multiplexing (SDM) multiple-input--multiple output (MIMO) detector, sphere decoder, wireless systems.

In orthogonal-code hopping multiplexing (OCHM) systems, hopping-pattern (HP) collisions may degrade system performance. Previous studies on the effect of HP collisions in OCHM systems were based on computer simulations, and there was no mathematical analysis of the bit-error-rate (BER) performance. The HP collisions in OCHM systems differ from hits in frequency-hopping systems or intracell interference in direct-sequence code-division multiple-access (DS/CDMA) systems because they can effectively be controlled through synergy and perforation techniques. In this paper, we introduce a received-signal model for OCHM systems called a perforation-only model and analyze the BER performance for OCHM systems in both uncoded and coded environments. Repetition, convolutional, and turbo codes are considered in coded environments. Through the analysis of BER performance, OCHM systems can more clearly be characterized, and the allocated power at the base station (BS) can be estimated for OCHM systems. Furthermore, the user capacity is analyzed for a given channel coding scheme. The results show that the uncoded BER is saturated by the perforation probability, and the coded BER is degraded as the perforation probability increases. We investigate the allocated power at the BS according to the perforation probability and compare the user capacities of OCHM systems using the three different types of coding schemes. Index Terms--Bit-error-rate (BER) analysis, convolutional codes (CCs), orthogonal-code hopping multiplexing (OCHM), power allocation, repetition codes (RCs), turbo codes (TCs), user capacity.

This paper introduces a layered structure of the Korean terrestrial digital multimedia broadcasting (T-DMB) ensemble based on Eureka-147 and suggests a new transmission architecture for flexible T-DMB service. In the suggested transmission architecture, MPEG-2 transport stream (TS) for T-DMB multimedia service is inserted into the ensemble distributed via the ensemble transport interface (ETI). Thus, we propose a novel algorithm remultiplexing the ETI with MPEG-2 TS. The architecture of ETI remultiplexing algorithm is described as a four-step process, and implemented as real-time embedded software in an ETI remultiplexing system. The design and implementation of the interoperable ETI remultiplexing system available for a small-scale transmission system for T-DMB service is described in detail. Index Terms--DAB, DMB, ensemble, ETI, Eureka-147, MPEG-2 TS, remultiplexing.

Space division multiple access (SDMA) with an antenna array at the transmitter is a promising means for increasing system capacity and supporting rate-demanding services. However, the presence of an antenna array at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on access layer channel allocation, reflected on channel reuse. This impact obtains different twists in TDMA, CDMA and OFDMA due to the different nature of co-channel and cross-channel interference and the different interaction of user spatial channel characteristics with system channels, namely time slots, codes and subcarriers. We consider these access schemes in a generalized unified framework and propose heuristic algorithms for channel allocation, downlink beamforming and transmit power control so as to increase total provisioned system rate and provide QoS to users in the form of minimum rate guarantees. We study the class of greedy algorithms that rely on criteria such as induced or received interference and signal-to-interference ratio (SIR), and a class of SIR balancing algorithms. Results show superior performance for SIR balancing resource allocation and expose the performance benefits of cross-layer design. Index Terms--Beamforming, SDMA, power control, cross-layer design, resource allocation, T/C/OFDMA.

Packet-switched unidirectional and bidirectional ring wavelength division multiplexing (WDM) networks with destination stripping provide an increased capacity due to spatial wavelength reuse. Besides unicast traffic, future destination stripping ring WDM networks also need to support multicast traffic efficiently. This article examines the largest achievable transmitter throughput, receiver throughput, and multicast through put of both unidirectional and bidirectional ring WDM networks with destination stripping. A probabilistic analysis evaluates both the nominal capacity, which is based on the mean hop distances traveled by the multicast packet copies, and the effective capacity, which is based on the ring segment with the highest utilization probability, for each of the three throughput metrics. The developed analytical methodology accommodates not only multicast traffic with arbitrary multicast fanout but also unicast and broadcast traffic. Numerical investigations compare the nominal transmission, receiver, and multicast capacities with the effective transmission, receiver, and multicast capacities and examine the impact of number of ring nodes and multicast fanout on the effective transmission, reception, and multicast capacity of both types of ring networks for different unicast, multicast, and broadcast traffic scenarios and different mixes of unicast and multicast traffic. The presented analytical methodology enables the evaluation and comparison of future multicast-capable medium access control (MAC) protocols for unidirectional and bidirectional ring WDM networks in terms of transmitter, receiver, and multicast throughput efficiency. Index Terms--Average hop distance, destination stripping, multicast, ring network, spatial wavelength reuse, wavelength division multiplexing (WDM).

We propose a low-complexity closed-loop spatial multiplexing method with limited feedback over multi-input--multi-output (MIMO) fading channels. The transmit adaptation is simply performed by selecting transmit antennas (or substreams) by comparing their signal-to-noise ratios to a given threshold with a fixed nonadaptive constellation and fixed transmit power per substream. We analyze the performance of the proposed system by deriving closed-form expressions for spectral efficiency, average transmit power, and bit error rate (BER). Depending on practical system design constraints, the threshold is chosen to maximize the spectral efficiency (or minimize the average BER) subject to average transmit power and average BER for spectral efficiency) constraints, respectively. We present numerical and Monte Carlo simulation results that validate our analysis. Compared to open-loop spatial multiplexing and other approaches that select the best antenna subset in spatial multiplexing, the numerical results illustrate that the proposed technique obtains significant power gains for the same BER and spectral efficiency. We also provide numerical results that show improvement over rate-adaptive orthogonal space-time block coding, which requires highly complex constellation adaptation. We analyze the impact of feedback delay using analytical and Monte Carlo approaches. The proposed approach is arguably the simplest possible adaptive spatial multiplexing system from an implementation point of view. However, our approach and analysis can be extended to other systems using multiple constellations and power levels. Index Terms--Adaptive modulation, bit error rate (BER), feedback delay, multi-input-multi-output (MIMO) systems, spatial multiplexing, spectral efficiency, substream selection.

We consider transmission of a continuous amplitude source over an L-block Rayleigh-fading [M.sub.t] x [M.sub.r] multiple-input multiple-output (MIMO) channel when the channel state information is only available at the receiver. Since the channel is not ergodic, Shannon's source-channel separation theorem becomes obsolete and the optimal performance requires a joint source-channel approach. Our goal is to minimize the expected end-to-end distortion, particularly in the high signal-to-noise ratio (SNR) regime. The figure of merit is the distortion exponent, defined as the exponential decay rate of the expected distortion with increasing SNR. We provide an upper bound and lower bounds for the distortion exponent with respect to the bandwidth ratio among the channel and source bandwidths. For the lower bounds, we analyze three different strategies based on layered source coding concatenated with progressive superposition or hybrid digital/analog transmission. In each case, by adjusting the system parameters we optimize the distortion exponent as a function of the bandwidth ratio. We prove that the distortion exponent upper bound can be achieved when the channel has only one degree of freedom, that is L = 1, and min {[M.sub.t], [M.sub.r]} = 1. When we have more degrees of freedom, our achievable distortion exponents meet the upper bound for only certain ranges of the bandwidth ratio. We demonstrate that our results, which were derived for a complex Gaussian source, can be extended to more general source distributions as well. Index Terms--Broadcast codes, distortion exponent, diversity-multiplexing gain tradeoff, hybrid digital/analog coding, joint source--channel coding, multiple-input multiple-output (MIMO), successive refinement.

Multiple-input multiple-output (MIMO) spatial multiplexing that needs to separate and detect transmitted signal streams by using processing at the receiver end can increase the data rates of transmissions on independent and identically distributed (i.i.d.) channels. Such channels have been considered to exist in nonline-of-sight (NLOS) environments. However, actual communications may also be conducted in line-of-sight (LOS) environments. While an LOS component can increase the received power level, it may also cause correlated channels that make it difficult to detect the transmitted streams. In this paper, we describe the performance of 4 x 4 MIMO spatial multiplexing based on LOS and NLOS channel measurements in an indoor environment. For eight configurations of uniform linear arrays (four antenna spacings and two array orientations), we evaluated the cumulative distribution function (CDF) of the channel capacity and bit error rate performance versus transmit power, and we analyzed them in terms of antenna pattern, fading correlation, CDFs of MIMO channel elements, and CDFs of eigenvalues. Results show that, despite higher fading correlations and non i.i.d, channel characteristics, the performance of MIMO spatial multiplexing in the LOS environment is better than that in the NLOS one. However, the performance in the measured LOS environment largely depends on the MIMO configuration. Index Terms--Array element pattern, bit error rate (BER), channel capacity, channel element distribution, eigenvalue distribution, fading correlation, indoor channel measurement, multiple-input multiple-output (MIMO), mutual coupling, spatial multiplexing.