This letter introduces a closed form expression for the channel capacity increase achieved by adding a new pair of transmit and receive antennas. By analyzing this expression, an iterative transmit/receive antenna selection algorithm of low computational complexity is proposed. The new algorithm has higher computational complexity than some existing algorithms, but as the results show, the performance improvement of the proposed algorithm approaching more to the optimal algorithm.

We present an orthogonal frequency division multiple access (OFDMA) based multichannel slotted ALOHA for cognitive radio networks (OMSA-CR). The performance of an infinite population based OMSA-CR system is analyzed in terms of channel capacity, throughput, delay, and packet capture effect. We investigate the channel capacity for OMSA-CR with perfect or imperfect spectrum sensing. We introduce the proposed CR MAC based on two channel selection schemes: non-agile channel selection (NCS) and agile channel selection (ACS). Comparing them, we show the tradeoff between complexity and system performance. We verify the proposed CR system model using numerical analysis. In particular, using simulation with a finite populated linear feedback model, we observe the OMSA-CR MAC tradeoff between throughput and minimum delay whose results matched those of the analytical framework. Numerical results for the proposed system throughput are also compared to conventional MACs, including pure ALOHA based CR MAC.

Multiple-input multiple-output (MIMO) repeater systems have been discussed in several published papers. When a repeater has only one antenna element, the propagation environment is called keyhole. In this kind of scenario the achievable channel capacity and link quality are decreased. Another limit is when the number of the antenna elements of a repeater is larger than that of a MIMO transceiver, the channel capacity cannot be increased. In this paper, in order to obtain an upper bound of the channel capacity, we express a propagation process of the distributed MIMO repeater system with amplify-and-forward method by the numerical formular, and optimize the position of each repeater.

In this letter, the cumulative distribution function (CDF) for the maxima of the OSTBC-MIMO channel capacity in a temporal interval is estimated using the first-order Rice series approximation. As the estimation of the maxima distribution using the Rice series is applicable only to Gaussian random processes, the Gaussian-approximated probability density function (PDF) for the OSTBC-MIMO channel capacity is derived from existing exact PDF (non-Gaussian). The resulting CDF for the maxima capacity is useful to design OSTBC-MIMO systems.

The use of directional antenna and polarization diversity techniques has been reported to achieve good MIMO performance. Low-profile, small structures are required to configure the MIMO antenna with these techniques. First, we assume downlink transmission in indoor MIMO systems and present the design guidelines for the radiation pattern to obtain large channel capacity by the ray-tracing method. We then propose a uni-directional, dual-polarized MIMO antenna with a thickness of 0.24λ based on the design guidelines. The proposed antenna consists of dipole antennas mounted horizontally to the ground plane and cavity backed slot antennas for vertical polarization. We apply the proposed antenna to 2 2 MIMO transmission and demonstrate the effectiveness of channel capacity enhancement in an actual environment. The improvement factor is revealed to be +16.2% with place averaged value compared to sleeve antenna configuration.

In this paper, joint water filling and maximal ratio transmission (joint WF-MRT) downlink transmit diversity for a single-carrier distributed antenna network (SC DAN) is proposed. The joint WF-MRT transmit weight allocates the transmit power in both transmit antenna dimension and frequency dimension, i.e., the power allocation is done both across frequencies based on WF theorem and across transmit antennas based on MRT strategy. The cumulative distribution function (CDF) of the channel capacity achievable by joint WF-MRT transmit diversity is evaluated by Monte-Carlo numerical computation method. The channel capacities achievable with joint WF-MRT, MRT, and WF transmit weight (WF transmit weight is done across transmit antennas and frequencies based on WF theorem) are compared. It is shown that the joint WF-MRT transmit weight provides the highest channel capacity among three transmit weights.

In this letter, a new exact expression of the ergodic channel capacity for a Rician fading channel is provided that is written in terms of exponential integral and incomplete gamma function. Also, a good approximation of the Rician fading channel capacity is derived from the exact expression and its accuracy is numerically verified.

In this paper, the exact distribution of the channel capacity of MISO (multiple-input single-output) systems subject to co-channel interference is derived from an information theoretic viewpoint. It is found that the MISO channel capacity in the interference-limited channel follows the F-distribution. By using these capacity distributions, the outage capacity in Rayleigh fading channels can be accurately computed. We confirm the accuracy of our analysis by performing simulations. Our results exactly match those of the empirical simulations of interference-limited systems.

Multiuser -- Multiple Input Multiple Output (MU-MIMO) techniques were proposed to increase spectrum efficiency; a key assumption was that the Mobile Terminals (MTs) were simple with only a few antennas. This paper focuses on the Block Diagonalization algorithm (BD) based on the equal power allocation strategy as a practical MU-MIMO technique. When there are many MTs inside the service area of the access point (AP), the AP must determine, at each time slot, the subset of the MTs to be spatially multiplexed. Since the transmission performance depends on the subsets of MTs, the user selection method needs to use the Channel State Information (CSI) obtained in the physical layer to maximize the Achievable Transmission Rate (ATR). In this paper, we clarify the relationship between ATR with SU-MIMO and that with MU-MIMO in a high eigenvalue channel. Based on the derived relationship, we propose a new measure for user selection. The new measure, the eigenvalue decay factor, represents the degradation of the eigenvalues in null space compared to those in SU-MIMO; it is obtained from the signal space vectors of the MTs. A user selection method based on the proposed measure identifies the combination of MTs that yields the highest ATR; our approach also reduces the computational load of user selection. We evaluate the effectiveness of user selection with the new measure using numerical formulations and computer simulations.

A coordinate plane representation of the resource requirements of digital modulation methods is presented, and an overall resource efficiency measure is proposed. This measure can be used for the comparison of digital modulation methods and the evaluation of an emerging modulation technique. Several typical digital modulation methods are compared based on this measure to show its validity.

Orthogonal frequency division multiplexing (OFDM), which uses a number of narrowband orthogonal sub-carriers, is a promising transmission technique. Also multi-carrier code division multi-access (MC-CDMA), which combines OFDM and frequency-domain spreading, has been attracting much attention as a future broadband wireless access. It was shown that MC-CDMA has lower channel capacity than OFDM, due to inter-code interference (ICI) resulting from orthogonality distortion caused by frequency-selective fading. Recently, many ICI cancellers have been proposed to mitigate the effect of ICI. In this paper, we derive a channel capacity expression for MC-CDMA assuming perfect ICI cancellation taking into account both frequency diversity gain and space diversity gain and compare it to that of OFDM. Furthermore, we derive a channel capacity expression for the case of imperfect ICI cancellation to discuss the impact of the residual ICI.

To increase the transmission rate without bandwidth expansion, the multiple-input multiple-output (MIMO) technique has recently been attracting much attention. The MIMO channel capacity in a cellular system is affected by the interference from neighboring co-channel cells. In this paper, we introduce the cellular channel capacity and evaluate its outage capacity, taking into account the frequency-reuse factor, path loss exponent, standard deviation of shadowing loss, and transmission power of a base station (BS). Furthermore, we compare the cellular MIMO downlink channel capacity with those of other multi-antenna transmission techniques such as single-input multiple-output (SIMO) and space-time block coded multiple-input single-output (STBC-MISO). We show that the optimum frequency-reuse factor F that maximizes 10%-outage capacity is 3 and both 50%- and 90%-outage capacities is 1 irrespective of the type of multi-antenna transmission technique, where q%-outage capacity is defined as the channel capacity that gives an outage probability of q%. We also show that the cellular MIMO channel capacity is always higher than those of SIMO and STBC-MISO.

The effect of wall and indoor scatterers on the indoor multiple input multiple output (MIMO) communication system is investigated by using the hybrid technique of finite difference time domain (FDTD) method and method of moments (MoM). MIMO channel capacity with the wall reflection is investigated with consideration of the eigenvalue of channel covariance matrix, the received power and the effective multipaths of MIMO system. It is found that the stronger side wall reflection can lead to the higher MIMO channel capacity. MIMO system with indoor scatterers is also analyzed and compared with the line of sight (LOS) indoor MIMO system. It is found that the scatterer material has different effect on the received power and the effective multipaths of MIMO system.

MIMO leads to dramatic improvement in channel capacity and/or link reliability of wireless systems. However, a MIMO channel has only one degree of freedom in a keyhole environment. As a result, this environment reduces achievable channel capacity and link quality. This paper proposes a MIMO repeater system, which can realize a multi-stream transmission. Although the averaged channel capacity in the MIMO repeater system is discussed in several published papers, the probability density functions of eigenvalues of correlation matrix are not analyzed. MIMO transmission performance can basically be estimated from eigenvalues of the channel correlation matrix. We derive an approximated formula for the probability density function of all eigenvalues linked to the space diversity. It is shown that the calculated values based on the proposed method agrees very well with the simulated values.

This paper presents an investigation of radio-wave propagation characteristics in the 5 GHz band in a residential two-story house. We investigated the 3-D angular spectra of incident waves when a transmitter and a receiver were situated on the first and second floors, respectively. First of all, correlation in the measured "home environment" containing furniture such as beds, a sofa and tables was determined to confirm a quasi-static environment. Then, 3-D angular spectra measurements were performed by using an eight-element Yagi-Uda antenna as a receiving antenna. Furthermore, the 4-by-4 MIMO channel capacity at each elevation angle was estimated by using elevation angular spectra and the propagation characteristics between the first and second floors were evaluated. The results indicated that the channel capacity in the elevation direction was strongly influenced by the direction of the transmitting antenna.

A multi-input erasure channel is defined as the J(J+1) discrete memoryless channel, for which we study a capacity formula, through the method by Muroga. We first give a simpler capacity formula for the multi-input erasure channel with no cross probability. Next we give an upper bound to the capacity for the general case. Finally we remark that the upper bound is actually the capacity when the cross probability is small.

Multilink MIMO technique is a promising technology for cellular networks with a guaranteed quality-of-service. It will provide high capacity and wide coverage. We evaluated the downlink performance of the multilink MIMO system from the perspective of quality-of-service. The presence of Rayleigh fading, shadowing, and path loss was assumed. To evaluate the proposed system, we developed a performance measure for MIMO cellular system. The measure is ergodic capacity taking into account area coverage. Our numerical results show that the area coverage of proposed multilink MIMO system is greatly improved compared with that of the conventional singlelink MIMO system. Using the proposed measure, we also found that the multilink MIMO system could achieve high capacity with guaranteed QoS for a wide coverage.

MIMO systems using a space division multiplexing (SDM) technique in which each transmit antenna sends an independent signal substream have been studied as one of the successful applications to increase data rates in wireless communications. The throughput of a MIMO channel can be maximized by using an eigenbeam-SDM (E-SDM) technique, and this paper investigates the practical performance of 22 and 44 MIMO E-SDM based on indoor measurements. The channel capacity and bit error rate obtained in various uniform linear array configurations are evaluated and are compared with the corresponding values for conventional SDM. Analysis results show that the bit error rate performance of E-SDM is better than that of SDM and that E-SDM gives better performance in line-of-sight (LOS) conditions than in non-LOS ones. They also show that the performance of E-SDM in LOS conditions depends very much on the array configuration.

A numerical hybrid method for analyzing the wireless channel of Multiple-Input Multiple-Output (MIMO) communication system is proposed by combining of the method of moments (MoM) and the finite difference time domain (FDTD) method. The proposed method is capable of investigating a more practical MIMO wireless channel than the conventional methods, and CPU time is much less than that of the FDTD method in analysis of spatial statistical characteristics of received signals. Based on the channel transfer matrix obtained by the proposed method, the wall effect on indoor MIMO channel capacity are investigated with consideration of received power, Ricean K-factor and effective degrees of freedom (EDOF) of multipaths by changing the wall locations and material.

Antenna array is essential factor for multiple- input multiple-output (MIMO) wireless systems. Since the antenna array is composed of closely spaced elements, the mutual coupling among the elements cannot be ignored for the best performance of the array. Mutual coupling affects the MIMO channel, so the performance of a MIMO system, including channel capacity and diversity, varies with the degree of mutual coupling. The effect of mutual coupling is a function of the antenna load impedance. Therefore, designing an optimal element-matched array for a MIMO system requires consideration of the optimal matching condition for the array elements, the one that maximizes the channel capacity. We evaluated the effects of mutual coupling with various matching conditions in dipole arrays, and investigated their effects on the path correlation and channel capacity of MIMO systems. Simulation showed that the conventional conjugate matching of each element is still suitable for closely spaced elements except when the separation is about less than 0.1λ. Theoretical consideration of the received power of a closely-spaced-element array is also provided to show the effects of mutual coupling.