| 1. |
- Persson, Patrik, et al.
(författare)
-
Design and evaluation of a 2 x 2 MIMO repeater
- 2009
-
Ingår i: European Conference on Antennas and Propagation, EuCAP 2009, Proceedings. - 9783000245732 ; , s. 1509-1512
-
Konferensbidrag (refereegranskat)abstract
- In this paper the design and measurement-based evaluation of an amplify-and-forward 2 x 2 MEMO repeater is presented. During the design phase, simulations were made to study different scenarios and repeater parameter settings. The evaluation of the repeater was made using field trials in Kista, Stockholm, Sweden. Three scenarios were considered; coverage, outdoor-to-indoor, and LOS MEMO rank enhancement. The overall results showed good improvement in received signal strength, ranging from only a few dB up to 25 dB depending on the particular measurement scenario. Moreover, the concept of repeater-aided rank enhancement in LOS also showed good results.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Bohlin, Patrik, 1974
(författare)
-
Influence of Channel Estimation on Wireless Communication System Performance
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many wireless communication systems today employ receivers that use channel estimation as an integral part of the receiver chain. Two sides of this problem are studied in this thesis: Impact of channel estimation on low complexity receivers for multi antenna and CDMA systems, and the performance of systems based on superimposed pilots and systems with peak power constraints. First the connection between iterative least squares methods, relying on the finite alphabet properties of the transmitted signal, and the Expectation Maximization (EM) method is explored. A modification to the EM-algorithm known as SAGE, is proposed to be used in order to reduce the computational complexity and increase the performance. These algorithms are extended to cope with coded signals. By utilizing the extended distance between different codewords, significant performance gain can be seen. If a turbo code is employed for error protection, the complexity can be reduced even further by exploiting the iterative nature of the decoder. The last chapter in the first part is devoted to channel parameter estimation in a slotted DS-CDMA system. A near-far resistant estimator based on a large sample approximation to the maximum likelihood estimator is presented. The performance is evaluated by means of numerical simulations, and the estimator is also shown to be asymptotically efficient. In the second part the performance of training based and peak power limited systems is evaluated by means of channel capacity. The performance of MIMO-systems and systems with frequency selective channels are studied when the training is done in the form of SuperImposed Pilots (SIP). The parameters of the SIP scheme are optimized based on the mutual information, and the advantage of using superimposed pilots over conventional pilots is demonstrated for short coherence times. One issue with SIP is that the accuracy of the channel estimate is decreased. A method based on data aided channel estimation is proposed to mitigate this problem, and the proposed algorithm is found to perform close to the noncoherent channel capacity. Finally, the capacity achieving distribution for a Rayleigh fading system with peak power constraint is found. It is shown that a uniform phase and a discrete amplitude distribution is the optimal signalling scheme.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Bohlin, Patrik, 1974, et al.
(författare)
-
Performance Evaluation of MIMO Communication Systems based Superimposed Pilots
- 2004
-
Ingår i: IEEE International Conference on Acoustics, Speech, and Signal Processing; Montreal, Que; Canada; 17 May 2004 through 21 May 2004. - 1520-6149. ; 4, s. IV-425-IV-428-
-
Konferensbidrag (refereegranskat)abstract
- In the recent past, a number of publications have suggested superimposed pilots (SIP) for channel estimation in MIMO systems. However, the performance gain achieved by SIP compared to conventional (time-multiplexed) training is still questionable. In this paper we introduce a framework for modeling a general SIP scheme, of which the conventional scheme is a special case. Utilizing this framework, we derive a lower bound on the channel capacity to compare the performance between the two systems. It is found that in certain scenarios (high SNR, many receive antennas and short coherence times), it is beneficial to also transmit data during the training mode (i.e., use SIP). The main conclusion though, is that for most cases where these kind of schemes would be realistic, i.e. for systems with coherence lengths of more than a few symbols, the general SIP-scheme reduces to the conventional scheme. Hence, rendering the same capacity.
|
|
| 10. |
|
|
