As the demand for reliable high speed data transmission increases, the capacity of downlink cellular multiple-input multiple-output (MIMO) systems is of much interest. Unfortunately, the capacity analysis regarding the frequency reuse factor (FRF) is rarely reported. In this paper, theoretical analyses for both ergodic and outage capacities for cellular MIMO systems are presented. The FRF is considered and a hybrid frequency reuse scheme is proposed. It is shown by the numerical results that the proposed scheme can greatly alleviate the coverage problem of single-frequency-reuse cellular systems.

This paper proposes a VoIP (Voice over Internet Protocol) session capacity expansion method that uses periodic packet transmission suppression control for wireless LANs. The proposed method expands the VoIP session capacity of an AP without critically degrading the QoS (Quality of Service) of all stations. Simulation results show the proposed method with 0.5% packet suppression control on each station expands a VoIP session capacity by up to 5% compared to a legacy method while satisfying required QoS for all stations.

The capacity of multiuser OFDM systems can be maximized by allocating resources (subcarrier and power) to the user with the highest instantaneous channel gain. This assumes complete channel state information (CSI) at the transmitter, which is achieved by every user reporting its CSI for all subcarriers to the transmitter via feedback channel. In practice, due to the limited capacity of the feedback channel, the completeness of CSI may be severely restricted especially with a large number of users transmitting a large amount of feedback information. In order to reduce the amount of feedback information while preserving the maximal capacity, quality based CSI feedback (QCF) is proposed in this letter. The system capacity is derived with QCF and compared with that of full CSI feedback. The results show that QCF successfully reduces the amount of feedback information with little capacity loss.

The transmission of correlated messages over strong interference channels is examined. The result is the proposal of a single-letter characterization of the sum-rate capacity of strong interference channels with correlated messages. It is shown that if the messages are independent, the sum-rate capacity is equal to that of [1] obtained by Costa and El Gamal. However, it can be larger than that of [1] if the messages are correlated. It is also shown that, in terms of the sum-rate, the achievable rate region in [2] is indeed the sum-rate capacity.

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.

This paper describes the measurements made in an urban canyon environment of a relay network scenario to determine the capacity of the multiple-input-multiple-output (MIMO) channel. While varying antenna number and spacing, we measure the channel matrices in the 3.7 GHz band using a 44 switching MIMO channel sounder. The results show that antenna spacing is shown to have less impact than signal-to-noise (SNR) on MIMO channel capacity in a line-of-sight (LOS) environment when physical antenna spacing is selected at four wavelengths. As a result, in an urban MIMO LOS scenario, a base station can provide sufficient data throughput to relay station because most links from base station to relay station have LOS environment and are free from restriction of antenna spacing.

This paper derived a closed-form expression for inter-flow capacity of a backhaul wireless mesh network (WMN) with centralized scheduling by employing a ring-based approach. Through the definition of an interference area, we are able to accurately describe a bottleneck collision area for a WMN and calculate the upper bound of inter-flow capacity. The closed-form expression shows that the upper bound is a function of the ratio between transmission range and network radius. Simulations and numerical analysis show that our analytic solution can better estimate the inter-flow capacity of WMNs than that of previous approach.

MIMO (Multiple Input Multiple Output) communications systems equipped with array antennas at both the transmitter and receiver sides are a promising scheme to realize higher rate and/or reliable data transmission. In this paper, capacity analysis of MIMO Rayleigh channel with spatial correlation at the receiver of multipath taken into account is presented. In general, a model configuration of local scattering around a mobile station in MIMO environment is carried out by simulation to examine spatial correlation coefficients. Based on statistical properties of the eigenvalues of correlated complex random Wishart matrices, the exact closed-form expressions of distribution of the eigenvalues are investigated. Then, the general closed-form evaluation of integral form is proposed based on Meijer's G-function. The results demonstrate that the ergodic capacities are improved by increasing the number of the antennas and the SNR's. Compared with i.i.d. (independent identically distributed) Rayleigh channel, the incremental improvement of correlated Rayleigh channel is reduced by spatial fading correlation. The analytical results validated by Monte-Carlo simulations show a good agreement.

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.

In this letter, we develop a two-step receive antenna selection method to maximize channel capacity. Different from previous work, we first derive a lower bound on capacity based on Hadamard inequality and arithmetic-geometric mean inequality, which is then used to iteratively drop the worst-performing antennas according to their measure. The recursive nature of this method helps to largely reduce the computational complexity.

In virtual cellular network (VCN), proposed for high-speed mobile communications, the signal transmitted from a mobile terminal is received by some wireless ports distributed in each virtual cell and relayed to the central port that acts as a gateway to the core network. In this paper, we apply the multi-route MHMRC diversity in order to decrease the transmit power and increase the multi-hop link capacity. The transmit power, the interference power and the link capacity are evaluated for DS-CDMA multi-hop VCN by computer simulation. The multi-route MHMRC diversity can be applied to not only DS-CDMA but also other access schemes (i.e. MC-CDMA, OFDM, etc.).

This paper addresses the problem of maximizing the protocol capacity of 802.11e networks, under the assumption that each access category (AC) has the same packet length. We prove that the maximal protocol capacity can be achieved at an optimal operating point with the medium idle probability of , where Tc* is the duration of collision time in terms of slot unit. Our results indicate that the optimal operating point is independent of the number of stations and throughput ratio among ACs, which means the proposed analytical results still hold even when throughput ratio and station number are time-varying. Further, we show that the maximal protocol capacity can be achieved in saturated cases by properly choosing the protocol parameters. We present a parameter configuration algorithm to achieve both efficient channel utilization and proportional fairness in IEEE 802.11e EDCA networks. Extensive simulation and analytical results are presented to verify the proposed ideas.

In this letter, we propose that directional antennas, combined with power management, be incorporated to reduce intersystem interference in a shared band overlaid high altitude platform station (HAPS)-terrestrial code division multiple access (CDMA) system. To eliminate the HAPS to terrestrial interference, the HAPS is accessed only via directional antennas under the proposed scheme. By doing so, the uplink power to the HAPS can accordingly be increased, so that the terrestrial to HAPS interference is also effectively suppressed.

The low complexity tree-structure based user scheduling algorithm is extended into up-link MLD-based multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) wireless systems. The system sum capacity is maximized by careful user selection on a defined tree structure. The calculation load is reduced by selecting the M most possible best branches and sampling in frequency dimension. The performances of the proposed scheduling algorithm are analyzed within three kinds of OFDMA systems and compared with conventional throughput-based algorithm. Both the theoretical analysis and simulation results show that the proposed algorithm obtains better performance with much low complexity.

Most studies into multiple-input multiple-output (MIMO) antenna systems have aimed at determining the capacity-achieving (CA) input covariance given a certain degree of channel state information (CSI) at the transmitter and/or the receiver side. From the practical perspective, however, there is a growing interest in investigating the scenario where the system performance is power-limited as opposed to rate-limited. Of particular concern is the open problem of solving the optimal power-saving (PS) input covariance for spatially correlated MIMO channels when only the long-term (slow-varying) channel spatial covariance information is available at the transmitter. In an attempt to achieve this goal, this paper analyzes the characteristics of the optimal PS input covariance given the knowledge of channel spatial covariance information and the rate constraint of the transmission. Sufficient and necessary conditions of the optimal PS input covariance are derived. By considering the large-system regimes, we further devise an efficient iterative algorithm to compute the asymptotic optimal PS input covariance. Numerical results will show that the asymptotic solution is very effective in that it gives promising results even for MIMO systems with only a few antennas at the transmitter and the receiver.

The use of frequency-domain equalization based on minimum mean square error criterion (called MMSE-FDE) can significantly improve the bit error rate (BER) performance of DS-CDMA signal transmission compared to the well-known coherent rake combining. However, in a DS-CDMA cellular system, as a mobile user moves away from a base station and approaches the cell edge, the received signal power gets weaker and the interference from other cells becomes stronger, thereby degrading the transmission performance. To improve the transmission performance of a user close to the cell edge, the well-known site diversity can be used in conjunction with FDE. In this paper, we consider DS-CDMA downlink site diversity with FDE. The MMSE site diversity combining weight is theoretically derived for joint FDE and antenna diversity reception and the downlink capacity is evaluated by computer simulation. It is shown that the larger downlink capacity can be achieved with FDE than with coherent rake combining. It is also shown that the DS-CDMA downlink capacity is almost the same as MC-CDMA downlink capacity.

In this paper, we propose a converting technique based method to solve nonlinear multi-commodity network flow (NMNF) problems with a large number of capacity constraints and discuss the associated implementation. We have combined this method with a successive quadratic programming (SQP) method and a parallel dual-type (PDt) method possessing decomposition effects. We have tested our method in solving a kind of lattice-type network system examples of NMNF problems. The simulation results show that the proposed algorithm is efficient for solving NMNF problems and successfully handles a large number of coupling capacity constraints. Furthermore, the computational efficiency of the proposed algorithm is more significant while the numbers of capacity constraints are increased.

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.

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.