Research On Key Technologies Of Distributed Antenna Placement Optimization For Mobile Communications Networks

As a significant feature of the future mobile communications networks, distributedmultiple antennas systems can achieve high channel capacity, decrease the transmitpower and enhance the cell coverage. Therefore, distributed multiple antennas systemshave become research hotspot in recent years. For the distributed multiple antennassystems, antennas are placed in different locations, so the first problem to be solved ishow to place antennas to obtain the best performance. However, research in this area isstill insufficient.We focus on two kinds of typical distributed multiple antennas systems: distributedtransmit antenna systems and cooperative relay systems. For the distributed transmitantenna systems, we investigate the antenna location optimization for antenna selectionsystem and indoor distributed space time block coding (STBC) system from theperspective of bit error ratio (BER). For the cooperative relay systems, we investigatethe relay location optimization for amplify-and-forward (AF) cooperative relaying overcorrelated shadowed fading channels and decode-and-forward (DF) automatic repeatrequest (ARQ) relaying over fast Rayleigh fading channels from the perspective ofoutage probability. The details of the investigation are as follows:Firstly, we present the downlink antenna selection strategies and derive the symbolerror ratio for the distributed transmit antennas systems, considering a circular cell withthe radius of R and with antenna circular layout. Then optimal distributed antennaradius can be obtained by minimizing cell averaged symbol error ratio (CASER). Wetake selecting one antenna and selecting two antennas for example to illustrate ourproposed method. Numerical and simulation results show that the optimal antennaradius depends on the path loss exponent, the total number of distributed antennas andthe number of selected antennas. In particular, when the total number of antennas is6,the number of selected antennas is2, and the path loss exponent is3, the optimal radiusof the distributed antenna is0.65R.Secondly, the area averaged symbol error ratio (AASER) for indoor STBC downlinkwith distributed transmit antennas is derived, considering the effects of path loss,shadow fading and Rician fading. Then optimal antenna location can be obtained byminimizing AASER. Theoretical analyses show that the optimal antennas location isrelated to the room length a, width b, height c and the height of the mobile station h.When a2b212(c h)2≤0, the distributed antennas degenerate into the centralizedantennas. When a2b212(c h)2>0, two antennas should be located on the longitudinaldirection of the central axis of the room, and should be symmetrical about the center ofthe roof. Furthermore, the distance from the distributed antenna to the center of the roof Thirdly, we investigate the relay placement and power allocation for AF cooperativerelaying. Considering the joint effects of path loss, correlated shadowing, and flatRayleigh fading, we first derive the approximate outage probability in the highsignal-to-noise ratio (SNR) regime. Then three optimization problems are formulated tominimize the obtained approximate outage probability, namely, optimal relay placementwith fixed power allocation, optimal power allocation with fixed relay location, andjoint optimization of relay placement and power allocation. It is shown by the analyticaland numerical results that the correlation coefficients and the standard deviations ofshadowing have significant impacts on the optimal relay placement and powerallocation. As such, the impact of the correlated shadowing cannot be ignored. Theoptimal relay position may not be on the line connecting the source and the destinationfor certain scenarios. Furthermore, the joint optimization obtains the best outageperformance.Finally, we investigate the power allocation and relay placement for cooperative ARQrelaying over fast Rayleigh fading channels, where the channel gains are constantduring each ARQ transmission round and change independently from round to round.We derive the asymptotically tight approximation of outage probability in the high SNRregime. Furthermore, three optimization problems are formulated to minimize theobtained asymptotic outage probability, namely, optimization of the power allocation atthe source and the relay with fixed relay placement, optimization of the relay placementwith fixed power allocation, and joint optimization of the power allocation and relayplacement. It is shown that the cooperative ARQ relaying has4dB gain at outageprobability of10-3compared to direct transmission, and the maximum number of ARQrounds and the path loss exponent will impact the optimal power allocation and relayplacement.The research results in this dissertation provide feasible schemes for distributedantennas placement from the perspective of system BER and outage probability, whichcan be applied to the future distributed mobile communications networks.