MIMO systems appear to be very promising since they can provide high data-rate services. Moreover, they can greatly increase the channel capacity in a sufficiently scattering-rich environment by utilizing spatial diversity. With the intention of de- signing a real MIMO wireless communication system and predicting its perfor- mance, it is necessary to develop accurate and realistic MIMO channel models for different propagation scenarios. Therefore, this chapter pays special attention on the
Modeling Outdoor MIMO Radio Propagation Channels 21 MS BS Local scatterer ) ( m T S MS BS Local scatterer ) ( n R S
Figure 2.6: Waves impinging on the receiver bounced separately by local scatterers ST(m)around the transmitter or local scatterers S(n)R around the receiver.
modeling of MIMO mobile fading channels for outdoor propagation environments. The chapter began by highlighting the advantages of the geometry-based chan- nel modeling approach. Thereafter, different types of geometry-based channel mod- els were briefly reviewed. The literature study revealed that both non-isotropic scattering as well as M2M fading have been taken into account when develop- ing narrowband outdoor geometry-based MIMO channel models. However, for the wideband case, geometry-based channel models have been proposed only for isotropic scattering environments under the assumption that only the MS is moving. Motivated by these facts, Chapter 2 aimed at proposing new wideband geometry- based MIMO channel models for non-isotropic scattering environments as well as for M2M channels.
The chapter then summarized the work presented in Paper I (Appendix A), which deals with the topic of developing wideband geometry-based channel models for non-isotropic scattering propagation scenarios. In Paper I, a wideband one-ring MIMO reference channel model has been developed for non-isotropic scattering environments. A deterministic simulation channel model, which is required for
computer simulations, has directly been obtained from the reference model by us- ing the principle of deterministic channel modeling. Analytical expressions have been presented for the temporal ACFs, the 2D space CCFs, and the FCFs of both the reference model and the deterministic simulation model. It has been shown by theory, confirmed by simulations, that the statistical properties of the determinis- tic simulation model match those of the reference model very well. In addition, to demonstrate the usefulness of the derived deterministic simulation channel model, a space-time block coded MIMO OFDM system has been further simulated, where channel fading behavior is described by the developed wideband one-ring deter- ministic simulation channel model. The simulation results have confirmed the fact that the symbol transmission error rate performance improves with increasing the antenna spacing. The wideband one-ring channel simulators designed with a single scatterer in each cluster is obviously sufficient to guarantee an accurate evaluation of the MIMO-OFDM system performance in non-isotropic scattering environments if the number of discrete paths is sufficiently large. It should be mentioned that the procedure of deriving the wideband one-ring model is quite general and applicable to any given delay PSD. Such a procedure guarantees that the delay PSD of the obtained wideband channel models is identical to a given delay PSD. The resulting wideband deterministic channel model can be used to study the impact of the chan- nel parameters on the performance of wideband wireless communication systems under non-isotropic scattering conditions.
Afterwards, Chapter 2 summarized the work of developing wideband geometry- based channel models for MIMO M2M fading channels. Details regarding this work are reported in Paper II (Appendix B). In Paper II, the narrowband two-ring MIMO channel model based on double-bounce scattering has been extended with respect to frequency selectivity. A new geometrical two-ring reference model under the as- sumption of single-bounce scattering has been derived for narrowband MIMO M2M fading channels. Thereafter, a further extension of the proposed single-bounce scat- tering two-ring channel model to frequency selectivity has been made. Closed-form solutions have been presented for the temporal ACF, the 2D space CCF, and the FCF. The proposed wideband reference models can be used as a starting point for the design of stochastic and deterministic MIMO channel simulators. The obtained channel models are useful for the design, test, and optimization of future wideband M2M communication systems. Moreover, these models are important for studying the channel capacity of wideband M2M channels under various propagation condi- tions specified by different PSDs.
Chapter 3
Modeling and Statistical
Characterization of Indoor Radio
Propagation Channels
3.1
Introduction
An appropriate channel model, which precisely describes the underlying propaga- tion characteristics, is a prerequisite for designing an efficient wireless communi- cation system and accurately predicting the system performance [102]. Due to this fact, several outdoor geometry-based channel models were developed in Chapter 2 for various types of outdoor wireless communication environments. As a continua- tion work in the field of channel modeling, Chapter 3 is concerned with the design and simulation of indoor propagation channels.
In order to assist the indoor channel characterization and modeling, numerous measurement tests have been conducted under a variety of indoor scenarios. Offices, corridors, building, and factories are examples of indoor scenarios from where ex- perimental data are measured. Measurement results have been reported in the litera- ture for various frequency bands, such as 900 MHz [7, 12, 138], 1.5 GHz [132, 163], 4–5.5 GHz [48, 133], 17–18 GHz [29, 133], and 60 GHz [29, 103, 182]. Based on these measurement results, many empirical indoor statistical channel models [46, 47, 138, 171, 182] have been developed. The advantage of empirical statistical mod- els is that they are capable of characterizing the realistic fading behavior since these models are developed on the basis of real-world measurements. By changing the values of their channel parameters, these empirical statistical models can simulate other indoor propagation environments. In order to determine the proper parameter values, however, extensive new measurement campaigns are needed to be carried
out. Such actions are expensive and time consuming. Alternatively, ray-tracing techniques [21, 75, 136, 139] can be exploited to simulate indoor propagation chan- nels. Ray-tracing techniques approximate the electromagnetic-wave propagation by generating all possible paths (rays) from the BS to the MS according to the rules of geometrical optics. Ray-tracing channel models [66, 69, 83, 157] can ef- ficiently capture the fading behavior of specified indoor environments. Many ray- tracing channel models developed so far have shown good agreement with measured channel characteristics [10, 79, 128]. Ray-tracing models, nonetheless, greatly de- pend on the physical layouts and materials through which signals propagate, e.g., walls, floors, and ceilings. On top of it, the main drawback of ray-tracing models is their computational cost, which relies on the size and complexity of the geographic database as well as the interaction order in a ray search. Therefore, the tradeoff between the prediction accuracy and the simulation efficiency has to be considered when modeling indoor propagation channels by means of ray-tracing techniques.
Both the empirical statistical channel models and ray-tracing channel models, have their own strengths and limitations when they are exploited to characterize in- door mobile radio propagation channels. To cope with the drawbacks mentioned above, a geometrical channel model has been proposed in [67] for indoor environ- ments, where it is assumed that scatterers are randomly distributed within a circle centered on the BS. However, the model developed in [67] is only applicable to the indoor environments where the distance between the BS and the scatterers fol- lows the exponential distribution. Moreover, it is not realistic to characterize an indoor scatterer region, like offices and walkpaths, by a circle. In contrast, a rect- angle is more appropriate to describe indoor propagation situations. Motivated by the scarcity of proper geometry-based indoor channel models, this chapter is dedi- cated to develop new geometry-based channel models for indoor radio propagation conditions. As a starting point, a novel geometrical rectangular scattering model is proposed in Section 3.2, from which a narrowband indoor channel model is derived. Section 3.3 will discuss the extension of the narrowband rectangle channel model obtained in Section 3.2 with respect to frequency selectivity.