Esa Kunnari

Performance analysis of multirate MC-CDMA in Rayleigh-fading channels with delay power spectrum exceeding the guard interval

Multicarrier code-division multiple access (MC-CDMA) is a promising multiplexing technique for future mobile radio systems, which require multirate transmission capability to efficiently support various services with wide range of data rates. In this paper, a generic performance analysis for the multicode and variable spreading factor multirate schemes in MC-CDMA is presented. Results comparing and pointing out notable differences in the error rate performance of these multirate schemes in conjunction with six different combining techniques are presented for the synchronous downlink and both the synchronous and asynchronous uplink. Furthermore, the analysis takes into account also the intersymbol interference caused by the multipath delay components exceeding the guard interval, which is commonly omitted in the literature.

Stochastic modelling of Rice fading channels with temporal, spatial and spectral correlation

A statistical characterisation of a small-scale fading mobile radio channel is presented and a fading simulator for the simulation of multiple input-multiple output multicarrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna positions and subcarrier frequency, leads to a tapped delay-line model with time, space and frequency-selective taps. The taps are modelled as a sum of a deterministic line-of-sight or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time-correlation shaping filtering and a space-frequency correlation transformation, respectively. The structure and details of the simulator are presented, and the simulator is shown to achieve good accuracy while retaining a reasonable computational complexity.

Joint power control, receiver beamforming and adaptive multi base station coordination for uplink wireless communications

We concentrate on the sum power minimization problem for the uplink of wireless cellular systems in this paper. Given a certain quality-of-service (QoS) constraint per mobile station (MS), the optimal power control and receiver beamforming are jointly considered with adaptive multi base station set (MBS) selection for joint reception. An iterative optimization algorithm is proposed accordingly. Although the problem is non-convex in general, it can always be optimally solved via the proposed algorithm as long as it is feasible. By changing the size of MBS, the system performance in terms of the transmit power over all MSs is evaluated through system level simulations. The results show that the transmit power can be significantly reduced even with a small size MBS, which is of a great interests for uplink communications.

Convolutionally coded multi-antenna transmission in WCDMA over frequencyselective Rayleigh fading channel

The convolutionally coded multi-antenna transmission technique proposed in Ban et al., (1997), for direct sequence code division multiple access (DS-CDMA) systems is studied in a wideband CDMA (WCDMA) system. The performance of the considered scheme operating over frequency-selective Rayleigh fading channels is evaluated by analysis and computer simulations. The multi-antenna transmission scheme is shown to provide performance improvement over single-antenna transmission when the fading is slow and the number of users is low. However, at high system loads the performance is pronouncedly limited due to additional interference between the antennas.

Performance evaluation of space-time codes in wideband CDMA over frequency-selective Rayleigh fading downlink channel

The performance of space-time block and trellis codes proposed for narrowband systems is evaluated in wideband code division multiple access (CDMA) system operating over a frequency-selective Rayleigh fading channel. The evaluation is done by both analysis and computer simulations. The considered space-time codes are shown to provide considerable performance improvement over uncoded single-antenna transmission at high signal-to-interference-plus-noise ratio (SINR), but at high system loads the performance is pronouncedly limited in frequency-selective channels due to increased interference.

LTE uplink power control and base station antenna down tilt in a 3D channel model

This paper examines the impact of the uplink power control and base station (BS) antenna down tilt on the system level performance in a realistic multicell three dimensional channel model. The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) adopts single carrier frequency division multiple access (SC-FDMA) as an air interface. The intra-cell interference is thus avoided but the inter-cell interference is still an issue. The system level performance depends not only on the transmitted power but also on the inter-cell interference level. Uplink power control scheme is used to limit the mobile station (MS) transmit power in order to reduce the interference. To evaluate the system performance, a realistic propagation environment is essential. We extend the IST WINNER II channel model (WIM II) in the elevation domain and includ the elevation beam pattern. We show mathematical expressions of link loss related to the BS-MS distance, down tilt angle, link loss, beam gain, and the effect of MS open-loop-controlled power. Based on the 3D channel model, the impact of BS antenna down tilt angle effect along with open loop power control scheme is studied.

A Rice Fading MIMO Multicarrier Channel Model

A statistical characterization of a small-scale fading mobile radio channel is presented, and a fading simulator for the simulation of multiple input multiple output (MIMO) multicarrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna locations, and subcarrier frequency, leads to a tapped delay line model with time, space, and frequency selective taps. The taps are modeled as a sum of a deterministic line-of-sight (LOS) or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time correlation shaping filtering and a space-frequency correlation transformation, respectively. The simulator is shown to achieve a good accuracy while retaining a reasonable computational load

Space-time coding combined with phase sweeping transmit diversity

Combining of space-time coded modulation (STCM) and phase sweeping transmit diversity (PSTD) is considered. The potential performance gain of space-time codes for fast fading channels can be utilized also in quasistatic fading channels by introducing quickened fading that can be obtained by employing PSTD. In addition to using separate PSTD antennas for each STCM signal, another approach where the additional PSTD antennas are shared between the STCM signals is proposed. Both approaches are shown to improve significantly the error rate performance of two considered space-time codes, which were proposed for fast fading channels, in slow Rayleigh fading.

Analysis of multirate MC-CDMA over multipath channels with delay spread exceeding the guard interval

In this paper, a generic performance analysis for the multicode and variable spreading factor (VSF) multirate schemes in a multicarrier code division multiple access (MC-CDMA) system is presented. In addition to the downlink channel, the analysis includes also both the synchronous and asynchronous uplink channels. Furthermore, the analysis takes into account the intersymbol interference (ISI) caused by the multipath delay components exceeding the guard interval, which is commonly omitted in the literature. Numerical results comparing and pointing out notable differences in the error rate performance of the two multirate schemes, different combining techniques, and spreading sequences are presented

Performance Analysis of OFDM based UWB Systems with a Frequency-Domain CDMA for Multiple SOPs

In this paper, a performance analysis for the frequency-domain code-division multiple-access (CDMA) of multiple simultaneously operating piconets (SOPs) in orthogonal frequency-division multiplexing (OFDM) based ultra-wideband (UWB) systems is presented. Two different strategies for the accommodation of multiples SOPs, namely, the variable spreading factor (VSF) scheme with minimal spreading and the multicode scheme with maximal spreading, were considered. The channel is assumed to be Rayleigh fading with exponentially decaying delay power profile. Furthermore, the analysis takes into account the intersymbol interference (ISI) caused by the multipath delay components exceeding the guard interval. Numerical results demonstrate that the frequency-domain CDMA can be employed to accommodate multiple SOPs while maintaining acceptable performance when a suitable subcarrier combining method is used. The VSF and multicode schemes result in a similar performance when the number of SOPs is large, while notable differences are pointed out when there are only a few SOPs.