This paper presents a simple multiple-input-multiple-output (MIMO) channel model that predicts the eigenvalue distribution and hence, the capacity of MIMO systems using vertically polarized and dual-polarized transmit-antenna configurations with dual-polarized receive antennas. The channel model is verified using broadband outdoor channel measurements taken by a 2 x 3 MIMO system in the 2.5 GHz band.

This paper presents outdoor propagation measurements together with derivative analysis, modeling, and simulation of the 2/spl times/2 fixed wireless multiple-input multiple-output (MIMO) channel. Experimental data were collected in the suburban residential areas of San Jose, CA, at 2.48 GHz by using dual-polarized antennas. Measurement results include the estimation of path loss, Rician K-factor, cross-polarization discrimination (CPD), correlation coefficients, and the MIMO channel capacity. An elaborate K-factor model that assumes variation over location, time, and frequency is developed. Distance-dependent CPD models of the variable and constant signal components are proposed. A generalized 2/spl times/2 MIMO channel model is then derived based on the correlation among the path loss, the copolarized K-factor, and the CPD's distribution of the constant and scattered signal components. Finally, the MIMO channel response is simulated using the newly developed model, and results are found to be well in agreement with measurements.

Multiple-input-multiple-output (MIMO) systems generally fall into two categories, depending on the kind of gain they provide: spatial multiplexing (SM) methods yield capacity gain and diversity methods yield link quality gain [measured here by the post-processing signal-to-noise ratio (SNR)]. We consider a set of systems from each category, quantify their gains analytically or via simulations, and show how these gains vary with the receiver input SNR and the numbers of antennas. The contribution of this work resides in both the closed-form analytical results and the numerical comparisons. We both highlight the benefits of using additional transmit antennas and provide comparisons among diversity-based and SM-based MIMO schemes. The analytical results are for a diversity-based scheme that combines selection diversity at the transmit side with maximum ratio combining (MRC) at the receive side, which we show to upper bound the SNR performance of other diversity-based schemes. We find that, for practical system parameters, the relevant SNR metric is 6-12 dB higher for the diversity-based schemes than for SM-based schemes. At the same time, SM-based schemes yield capacity metrics which range from 30% higher to double that of diversity-based schemes.

We present a general framework to quantify the data throughput capabilities of a wireless communication system when it combines: (1) multiple transmit signals; (2) adaptive modulation for each signal; and (3) adaptive array processing at the receiver. We assume a noise-limited environment, corresponding to either an isolated cell or a multicell system whose out-of-cell interference is small compared with the thermal noise. We focus on the user data throughput, in bits per second/Hertz (bps/Hz), and its average over multipath fading, which we call the user spectral efficiency. First, an analysis method is developed to find the probability distribution and mean value of the spectral efficiency over the user positions and shadow fadings, both as a function of user distance from its serving base station and averaged over the cell coverage area. We assume fading conditions and receiver processing that lend themselves to closed-form analysis. The resulting formulas are simple and straightforward to compute, and they provide a number of valuable insights. Next, we run Monte Carlo simulations, both to confirm the analysis and to treat cases less amenable to simple analysis. A key contribution of this paper is a simple formula for the mean spectral efficiency in terms of the propagation exponent, mean signal-to-noise ratio at the cell boundary, number of antennas, and type of coding. Under typical propagation conditions, the mean spectral efficiency using three transmit and three receive antennas ranges from 19.2 bps/Hz (uncoded) to 26.8 bps/Hz (ideally coded), highlighting the potential benefits of multiple transmissions combined with adaptive techniques. This is much higher than the spectral efficiencies for a link using a single transmitter and a threefold receive diversity under the same conditions, where the range is from 8.77 bps/Hz to 11.4 bps/Hz. Moreover, the latter results are not nearly as practical to achieve, as they can for large signal constellations that would be highly vulnerable to impairments.

We investigate the high spectral efficiency capabilities of a cellular data system that combines the following: 1) multiple transmit signals, each using a separately adaptive modulation; 2) adaptive array processing at the receiver; and 3) aggressive frequency reuse (reuse in every cell). We focus on the link capacity between one user and its serving base station, for both uncoded and ideally coded transmissions. System performance is measured in terms of average data throughput, where the average is over user location, shadow fading, and fast fading. We normalize this average by the total bandwidth, call it the mean spectral efficiency, and show why this metric is a useful representation of system capability. We then quantify it, using simulations, to characterize multiple-input multiple-output systems performance for a wide variety of channel conditions and system design options.

We describe a simulation study of a cellular system using multiple-input multiple-output (MIMO) antenna techniques along with adaptive modulation and aggressive frequency reuse. We show, for the case of 3 transmit and 3 receive antennas, how much MIMO systems outperform systems with receive-diversity-only when noise dominates. When co-channel interference from surrounding cells dominates, the differences shrink, as do the absolute numbers. We quantify these reductions for the specific cases studied, and discuss further areas of research.

The use of multiple element antennas-both transmitting and receiving-has great potential for increasing the capacity of wireless systems. The maximum capacity is computed for an "edge-excited" cell with 3 base sites and a subscriber terminal with a 3 element array, for line-of-sight channels. In an attempt to approach this capacity, we show that the use of innovative signal processing at the receiver (blind source separation technique) seems to allow the system to achieve a significant portion of this great capacity promised by information theory.