We present partial coordination strategies in a clustered cellular environment, evaluating the achievable rate in the downlink transmission. Block Diagonalization is employed for the coordinated users within the cluster to remove interference, while the interference from non-coordinated users remains. The achievable rate is evaluated resorting to an analytical expression conditioned on the position of the users in the cluster. A partial coordination approach is proposed to reduce the coordination complexity and overhead, where users close to the base station are not coordinated. Two approaches are considered, namely the non-coordinated users can be grouped and assigned separated resources from the coordinated ones, or they can be mixed.

We focus on the mean achievable rate per user of the coordinated base station downlink transmission in a clustered cellular environment, with transmit power constraints at the base stations. Block Diagonalization is employed within the cluster to remove interference among users while the interference from other clusters remains. The average achievable rate per user is evaluated considering the effects of the propagation channel and the interference and a theoretical framework is presented to provide its analytical expression, validated by simulation results with different power allocation schemes. As an application, the number of cells of the cluster that maximizes the mean achievable rate per user is investigated. It can be seen that in most of the cases a reduced cluster size, close to seven cells, guarantees a rate very close to the maximum achievable.

Quantum detection in an N-dimensional Hilbert space H involves quantum states and corresponding measure ment operators which span an r-dimensional subspace U of H, with r ≤ N. Quantum detection could be restricted to this subspace, but the operations in U are still redundant, since the kets have N components. By applying the singular-value decomposition to the state matrix, it is possible to perform a compression from the subspace U onto a "compressed" space U̅, where the redundancy is removed and kets are represented by r components. The detection can be perfectly reformulated in the "compressed" space, without loss of information, with a greatly reduced complexity. The compression is particularly attractive when r ≪ N, as shown with an example of application to quantum optical communications.

In a Coordinated Base Station Transmission scenario for the downlink, we propose a precoding scheme based on a MMSE criterion to manage the inter-user interference. In order to allocate the transmitted power to each user's signal, we set up an iterative procedure based on a modified waterfllling distribution, which approaches the optimal performance with a viable complexity with respect to the numerical optimization. A further simplification may be introduced, giving a simple iterative waterfilling scheme, at the expense of some performance loss. The performance is illustrated obtaining the achievable rates for different antenna configurations and different kinds of power constraints. A comparison with a Block-Diagonalization approach shows the advantage of MMSE, in particular at low SNR.

The phase noise effect in multiple-input-multiple-output systems employing orthogonal frequency division multiplexing is considered in a realistic scenario where the estimated channel matrix is affected by an error. The analytical SINR degradation due to phase noise and channel estimation is obtained for linear receivers (ZF and MMSE).

In this work the effect of phase noise in multiple-input-multiple-output systems employing orthogonal frequency division multiplexing is considered in a realistic scenario where channel estimation is not perfect, so that the channel matrix used at the receiver to perform demodulation is affected by an estimation error. In particular, it is shown that the actual degradation depends on the scheme employed in the receiver. The zero-forcing scheme, although giving a slightly worse performance for the perfectly known channel, proves to be more robust to the effects of channel estimation errors in the presence of phase noise.

The performance of an overlay Bluetooth and IEEE 802.11b (WiFi) network is considered in terms of quality of service parameters such as the packet latency, the packet error rate, and the throughput, in the presence of a vertical handover procedure, taking into account the mutual Bluetooth-WiFi interference and showing the influence of the main system parameters. The objective is to maximize the user QoS allowing the mobile to switch from a network to the other, with the so-called vertical handover. The basic idea is to activate the vertical handover, not on the basis of the received power level, but by the crossing of thresholds defined by the user profile, which comprises objective values for parameters such as the packet error rate and the packet delay. The results show that the use of the vertical handover procedure can lead to an improvement in the QoS parameters

Phase noise can be a major source of performance degradation in low-cost, low-bit-rate digital systems operating in the millimeter wavelength band. The use of code-division multiple access (CDMA) for several new applications is envisaged, and the study of the effects of phase noise shows that even CDMA systems exhibit a performance degradation comparable to that of standard modulation formats. The use of CDMA with a differential modulation at the chip level improves the system performance with a simpler demodulator at the expense of the enhancement of multiuser interference. In this paper we propose a new approach to CDMA modulation, and a possible solution is suggested to obtain a tradeoff between the performance degradation due to the phase noise and to the multiuser interference.

Handover in a Bluetooth scatternet is studied. The inquiry procedure defined by the Bluetooth standard to create and manage an ad-hoc network could also be used to perform handover, but is too slow to keep communication active. An on-demand procedure, based on accurate paging, is proposed. The parameters needed to perform the handover are exchanged when necessary, thus information is not required to be stored on the devices. The handover performance is studied by giving a statistical description of the time needed to terminate it. We show that handover in a reasonable time is feasible, and is suitable for many of the asynchronous communications applications envisaged for Bluetooth.

The effects of oscillator phase noise on the performance of digital transmission systems employing QAM are investigated. The model used for the phase noise is a Wiener-Levy process which allows a moment characterization of the filtered phase noise. The penalty introduced by phase noise on the error probability is evaluated and compared with the approximation of a constant phase error.

This paper presents the technique for channel sounding experiments carried out at the Hewlett-Packard Laboratories in Bristol. The channel sounding measurements were taken at 1.7225 GHz, a frequency similar to those used by DCS 1800 and DECT, and to those which will be employed by other emerging PCS standards. Due to the time-varying characteristics of these radio channels, it is important to reflect the variations of the channel impulse response in the experiments, since the average impulse response gives only limited information for the analysis of radio communication systems. The technique presented is based on a software correlation between the input and the output of the channel, and the dynamic performance achieved is better than that obtained with conventional techniques. In particular, unlike conventional correlation sounders, this technique does not suffer from the trade-off between dynamic range and maximum resolvable Doppler shift.