Pekka Ranta

Co-channel interference cancelling receiver for TDMA mobile systems

A method for co-channel interference cancellation in TDMA mobile systems exploiting the characteristics of mobile channels is proposed. The independently fading multipath channels provide a distinct waveform coding on each of the co-channel signals, which is a basis for signal separation in receivers. This enables the use of joint detection methods in receivers provided that accurate channel estimates can be obtained for all the cochannels. A joint detection and channel estimation algorithm for multiple co-channel signals are derived. The performance of the receiver is verified by simulations with the GSM system assuming that the strongest interferer is cancelled.

TDMA cellular network application of an interference cancellation technique

This paper studies the deployment of a co-channel interference cancellation technique in narrowband TDMA cellular networks. Particularly the case in which the strongest co-channel interferer is canceled in the receiver is investigated by network simulations. The potential gain can either be realized as higher system capacity or lower network outage rate. The receiver algorithm for interference cancellation is presented and its performance is simulated for the use of the capacity simulations. The capacity gain is shown in comparison with the network without interference cancellation.

Interference cancellation by joint detection in random frequency hopping TDMA networks

We address the problem of combining two potential capacity enhancing techniques in the future TDMA mobile systems: slow random frequency hopping between co-channel cells and interference cancellation of the dominant interferer by joint detection. The former technique is based on the averaging the interference between all users leading to the so-called interference diversity gain. The latter technique can enhance the receiver performance by performing joint demodulation for the desired and interfering signals. We study the combination of the two techniques by radio link and network simulations to quantify the total capacity gain.

Constant modulus single antenna interference cancellation for GSM

In cellular systems, interference suppression at the mobile receiver can be used to improve the downlink performance and capacity. We investigate single antenna interference cancellation (SAIC) at the receiver for a GSM/EDGE system with GMSK modulation. An interference suppression technique, which exploits the constant envelope property of the GMSK modulated signal, was proposed by Berangi et al in (Wireless Pets. Commun., Kluwer Acad. Pub., no.19, p.37-55, 2001). We observed that such technique is very sensitive to channel estimation error and hardly provides any gain when least square (LS) channel estimation is employed. Therefore, we study the performance of constant modulus single antenna interference cancellation (CM-SAIC) with multi channel estimation and show that significant performance improvement can be achieved. In the presence of a single dominant interfering signal, we obtain up to 7 dB gain in the TU3 channel.

Performance of dual antenna diversity reception in WCDMA terminals

In this paper the performance of a dual antenna reception in WCDMA downlink is studied on the link and network levels for circuit switched service of 64 kbps. An effect of penetration diversity terminals and channel parameters to potential diversity gain are investigated from a point of view of two receivers; dual antenna RAKE and a space-time chip equalizer. Results indicate that the penetration of diversity terminals should be large before the performance gain in link level can be turned into significant increase in system capacity.

Wireless Video Streaming over UWB

This paper presents a wireless video streaming system over Ultra Wide Band (UWB) radio. Wireless video steaming is not a possibility so far due to its high bandwidth requirements and high power consumption. With Ultra Wide Band (UWB), a low power, high speed radio technology standard developed by the WiMedia Alliance; the dream of wireless video streaming become true. By giving the fact of UWB, 480 Mbps with transmission mask of -41 dbm/MHz; the UWB supports uncompressed or lossless compressed video screen size up to SVGA (800x600x24) with 30 frames/second rate. This is an extraordinary achievement concerning wireless video application. This paper will introduce a demonstration system that uses a Nokia 7710 phone as a UWB transmitter and a projector as a UWB receiver. The demonstration is a result of collaboration between Nokia Research Center Helsinki and WiQuest Communications Inc. USA.

Interference rejection with a small antenna array at the mobile scattering environment

In this paper we study the effect of the scattering environment around the mobile on the performance of a two antenna array receiver that employs an adaptive interference rejection combiner (IRC). Two different scattering scenarios are considered. Firstly, scatterers are assumed to be independent for the desired and interfering signals and, secondly, scatterers are assumed to be the same for the desired and interfering signals. All the simulations are done with the GSM system.

Cochannel interference suppression for constant modulus signals

In this paper we investigate the single antenna interference cancellation (SAIC) for the GSM/EDGE system with the GMSK modulation. If the received signal is a superposition of the desired signal and constant modulus (CM) interference, the semi-blind method proposed by Berangi and Leung in 2001 can be used to suppress interference and thereby improve the receiver performance. However, they assume an ideal channel state information which is not available in practical cellular systems. Furthermore, the CM-SAIC algorithm is rather sensitive for channel estimation error and the suppression gain can be lost due to inaccurate estimation. For instance, the CM-SAIC with least squares (LS) channel estimation provides hardly any gain. Therefore we introduce a novel iterative channel estimation method based on the CM criterion. When combined with the CM-SAIC detector significant performance improvement can be achieved. In the presence of single dominant interfering signal we obtain up to 5 dB gain in TU3 channel.

Fast power control for GSM HBS using training sequences

We investigate the usage of fast power control (PC) in Global System for Mobile Communications (GSM) based home base station (HBS) system to alleviate Rayleigh fading for slow moving mobile stations (MS). Low-speed MSs suffer from Rayleigh fading most due to the long periods they spend in the fading dips. Especially, if the system does not employ other techniques to combat Rayleigh fading, such as frequency hopping (FH), the negative effects of the fading are serious. To implement the signalling for fast PC, we propose the usage of training sequences to transfer the power control information over the GSM radio interface. The benefits of this method are various: the transfer of the PC commands will be fast, reliable and the pay load of the frame is not wasted. The magnitude of the improvement was assessed by simulating the link using the COSSAP simulating tool. The conclusion was that the fast PC will increase the link capacity and partly compensates the lack of frequency hopping.

Application of dominant interference cancellation in street microcells

In street microcells, a cochannel interference problem arises especially at the street intersections without base station site where interference level can go up very rapidly due to the possible line-of-sight interference. To guarantee contiguous service quality in the street crossings rather conservative reuse distances should be selected at the expense of lower system capacity. In this paper we show that at the street intersections a single interfering signal dominates suggesting that interference cancellation of the dominant interfering signal is a potential method to overcome the problem. Accordingly, we apply joint detection of the desired and dominant interfering signal in the GSM system and evaluate the potential advantage in the Manhattan microcell environment. The results indicate that this technique enables very low reuse distances in the future high capacity microcellular systems.