Performance analysis of OSTBC based MIMO - OFDM systems over uncorrelated Nakagami-m fading channels | |
| Author | Ansari, Ejaz A. |
| Call Number | AIT Diss. no.TC-09-03 |
| Subject(s) | Space time codes MIMO systems Radio--Transmitters and transmission--Fading Orthogonal frequency division multiplexing |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Telecommunications, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. TC-09-03 |
| Abstract | Multiple-input multiple-output (MIMO) based orthogonal frequency division multiplexing (OFDM) is a promising technique employed in modern Wireless Communication Systems to yield higher data rate with low cost a nd relatively low power consumption. MIMO-OFDM systems utilizing orthogonal space time block codes (OSTBC) usually provide efficient spectrum usage, high capacity and exhi bit robustness against multi-path fading respectively. It is extensively used in several wireless standards like digital audio broadcasting ( DAB ) and digital terrestrial television broadcasting ( DVB-T ), discrete multi-tone ( DMT ) in US and digital subscriber loop ( x DSL) respectively. MIMO-OFDM systems utilizing M -ary quadrature amplitude modulation ( M -QAM) constellation forms an important component of several wireless standards such as IEEE 802.11 ( WLAN ), IEEE 802.16 ( WMAN ) and IEEE 802.15 ( WPAN ). It is revealed that channel model coefficients employed in these wireless standards follow either Nakagami- m or log-normal fading. Preference is given to employ Nakagami- m fading for channel coefficients in order to get the maximum advantage that it can model a wide range of environmental conditions by adjusting its fading parameters, namely m and average power of n th tap. Thus, this dissertation focuses on the performance analysis of MIMO-OFDM systems in case of M -ary one and two dimensi onal constellations using OSTBC by employing Nakagami- m fading model for the channel coefficients. Although the topic of MIMO-OFDM over different fading channels is well investigated, but its closed form symbol error rate ( SER ) expressions and performance results employing (OSTBCs) over uncorrelated frequency-selective Nakagami- m fading channels are still not available. The closed form expressions are extremely useful for evaluating system's performance without carrying out time consuming simulations. Similarly, the performance results are also highly beneficial for determining the system's performance in the sense that many practical wireless standards extensively employ MIMO-OFDM systems in conjunction with ( M -QAM) constellation. This dissertation thus, focuses on the performance analysis of OSTBC based MIMO-OFDM systems over uncorrela ted frequency-selective Nakagami- m fading channels. For this purpose, we therefore, derive exact closed form expressions for the SER of M -ary Gray- coded one and two dimensional constellations when an OSTBC is employed and N t transmit antennas are selected for transmission over frequency-selective Nakagami- m fading channels. First an exact closed-form of average SER expression of OSTBC based MIMO-OFDM system for M -ary phase shift keying ( M -PSK) using traditional probability density function ( PDF ) approach is derived. We then compute exact closed form average SER expressions for M -ary pulse amplitude modulation ( M -PAM) and ( M -QAM) (square) schemes respectively by utilizing this generalized result. These expressions ar e valid over both frequency-flat and frequency- selective Nakagami- m fading MIMO channels and can easily be evaluated without using any numerical integration methods. We also show that average SER of MIMO-OFDM system using OSTBC in case of frequency-selective Rayleigh fading channels remains independent to the number of taps, L of that fading channel and the performance of the same system for two-tap un-correlated Rayleigh and Nakagami- m fading channels is better than that of the correlated one. Moreover, Monte Carlo simulation of MIMO-OFDM system using multiple transmit and receive antennas for different modulations is also presented to validate our theoretical results. Finally, due to availability of closed form expressions, we further provide the performance results (not reported before in the literature) of MIMO-OFDM system over both frequency-flat and frequency- selective Nakagami- m fading channels employing ( M -QAM) using OSTBCs under the transmission rate equal to 1, 2 and 3 bit(s)/s/Hz, respectively. These results show in case of both frequency-flat and frequency-selective Nakagami- m fading channels that: • At transmission rate of 1 bit/s/Hz, MIMO-OFDM systems employing ( Q -PSK ≡ QAM) constellation and utilizing rate one-half codes, i-e., g 3 and g 4 outperforms the same systems utilizing B -PSK and B -FSK modulations with Alamouti code, g 2 . • Similarly, at transmission rate of 2 bits/s /Hz, MIMO-OFDM systems employing gray-coded 16-QAM constellation and utilizing rate one-hal f codes outperforms the same systems using QAM modulation with full rate code, g 2 at high SNR s. But for low SNR s, we tend to observe the opposite phenomenon between the above two systems utilizing these constellations and the same OSTBCs. • Finally, at transmission rate of 3 bits/s/Hz, MIMO-OFDM systems employing gray-coded 16-QAM constellation and utilizing rate three-quarters codes, i-e., ( h 3 and h 4 ) outperforms the same systems using 8-PSK m odulation with fu ll rate code, g 2 at high SNR s. But for low SNR s, we tend to observe the opposite phenomen on between the two sy stems utilizing these constellations and the same OSTBCs. In this dissertation, we have also discussed the applications of our theoretical results towards SIMO-OFDM systems (i-e., diversity receivers using MRC ) and Cooperative based relaying systems in case of single relay network. For this purpose, we compared the performance of MIMO-OFDM system with SIMO-OFDM system by considering two transmit antennas (i.e., Alamouti Code, g 2 ) and N r receive antennas for equal energy constellation symbols like M -PSK. We explicitly stated the condition after carrying out the above analysis that the performance of the two systems remain the same provided we employ one transmit antenna and 2 N r receiving antennas at the receiving end for MRC . We also considered three time based (TDMA) protocols (I, II, III) under amplify and forward ( AF ) mode and did the performance analysis of the Cooperative Relay Network employing these three protocols over uncorrelated Nakagami- m fading channels. In order to overcome the complexity and make the problem tractable, we considered uncorrelated frequency- selective Rayleigh fading ( m = 1) as a special case among various taps of the channels to have the solutions in closed forms. We made the comparison of the system in case of three protocols by considering instantaneous signal -to-noise ratio, capacity and unconditional SER respectively. |
| Year | 2009 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. TC-09-03 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Rajatheva, R. M. A. P. |
| Examination Committee(s) | Ahmed, Kazi Mohiuddin;Poompat Saengudomlert;Guha, Sumanta;Adachi, Fumiyuki |
| Scholarship Donor(s) | Higher Education Commission (HEC), Pakistan;AIT Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2009 |