Tapani Ristaniemi

Jammer suppression in DS-CDMA arrays using independent component analysis

We propose using Independent Component Analysis (ICA) as an advanced pre-processing tool for blind suppression of interfering jammer signals in direct sequence spread spectrum communication systems utilizing antenna arrays. The role of ICA is to provide a jammer-mitigated signal to the conventional detection. If the jammer signal is weak or absent, preprocessing by ICA is not advisable. Therefore we also consider two possible switching schemes, called pre-switching and post-switching, which activate the ICA-based jammer canceller only when it is expected to improve conventional detection. ICA-RAKE pre-switching is less complex, while post-switching performs better, especially when the jammer is pulsed in nature. Simulations are given to illustrate the achieved performance gains for single- and multi-path channels.

DPCCH Gating Gain for Voice Over IP on HSUPA

In this paper, the concept of DPCCH (dedicated physical control channel) gating for HSUPA (high speed uplink packet access) is analyzed. DPCCH gating technique has been recently under consideration within WCDMA to inactivate control channels during no data transmission periods, and hence, not to misuse capacity. In order to study the concept benefit, a concrete real-time service is selected in this paper: Voice over IP (VoIP) for mobile communications. It will be shown that VoIP would be highly beneficed by DPCCH gating inclusion in 3GPP specifications. Both analytical and simulation studies were run to confirm the gain expectations.

Performance of receive diversity and LMMSE chip equalization in WCDMA HSDPA network

More advanced receiver structures than the conventional single antenna Rake can be used to improve the signal-to-noise (SNR) ratios, which is especially beneficial in order to utilize the high bit rates provided by the HSDPA concept in Wideband Code Division Multiple Access (WCDMA) network. In WCDMA system, orthogonal Walsh–Hadamard sequences are used as channelization codes. In frequency-selective fading channels the orthogonality of channelization codes disappears and intra-cell multiple access interference (MAI) arises. In order to mitigate the effect of MAI, chip-level equalization has shown to be a simple and effective solution. The effectiveness of chip equalization, however, degrades at the cell borders where the inter-cell interference dominates rather than MAI. Dual antenna reception is a straight-forward solution to mitigate that performance drop. In this paper, we present an analysis of the expected gains of advanced receivers over conventional single antenna Rake receiver in realistic situations by using a dynamic WCDMA system-level tool. Considered advanced receivers include single and dual antenna Linear Minimum Mean Squared Error (LMMSE) chip-level equalizers and dual antenna Rake receiver. The network performance with advanced receivers is studied also from a more practical point of view by assuming that the penetration of advanced HSDPA terminal receivers is gradually increased in the network.

Independent component analysis using successive interference cancellation for oversaturated data

In this paper, advanced interference cancellation strategies are considered and applied in DS-CDMA uplink receivers. Namely, we introduce a new successive interference cancellation (SIC) scheme in which blind source separation (BSS) techniques based on independent component analysis (ICA) are considered. Our main emphasis is on the oversaturated data in which situation easily arises for example in DS-CDMA systems when the number of active connections/users is high compared to number of chips per bit being used, that is, a highly loaded system. Proposed receiver structures combine the main benefits of pure BSS/ICA and SIC methods: (i) inherent mitigation of various types of interference sources by BSS/ICA, (ii) robustness against parameter estimation errors due to BSS/ICA, (iii) greatly improved interference suppression capability due to novel combination of SIC ideology and ICA for oversaturated data. The last item in the list can also be seen as a way to somewhat circumvent the ‘more sources than sensors’—problem, which is a challenging problem in BSS area. Numerical experiments with DS-CDMA uplink data are given to illustrate the achieved gains in capacity and bit-error-rate performance compared to conventional successive and parallel interference cancellation (PIC) schemes as well as more an advanced LMMSE-PIC receiver and variants of BSS/ICA techniques alone. Copyright

Signaled step size for downlink power control of dedicated channels in UTRA TDD

This paper discusses downlink inner loop power control in UTRA TDD. The current UTRA TDD downlink power control is similar to one in UTRA FDD mode, but due to the time division feature of TDD it can not operate as fast as in FDD and it is affected by rapid changes in environment. In this paper an improvement for the downlink inner loop power control algorithm is presented in which the power control step size is based on the difference between UE measured SIR and target SIR. This difference is then signaled from UE to UTRAN. Since the effectiveness of this algorithm depends on available signaling bandwidth that is used, dynamic system simulations are carried out to find out how many bits are needed for the signaling and how this algorithm is affected by signaling and measurement errors.

Joint Multipath Delay Tracking and Interference Cancellation in DS-CDMA Systems Using Successive ICA for Oversaturated Data

A recent idea is to use blind source separation (BSS) methods within successive interference cancellation (SIC) in DS-CDMA reception. This has been found to results in an interference cancellation solution, that is able to i) mitigate different kinds of interference sources (e.g. multi-access, multi-path and out-of-cell interferences) simultaneously, ii) tackle more sources than observations-problem and, consequently, operate in highly loaded systems and iii) deal with imperfect channel estimation better than conventional BSS receiver and conventional interference cancellation. Thus far however, a single path channel has been assumed in studies behind these findings. In this paper we extend our previous studies to multipath channels where inter-path interference hardens the joint delay tracking and interference cancellation problem even more.

Handover and Uplink Power Control Performance in the 3.84 Mcps TDD mode of UTRA Network

In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out.

On the Analytic Performance of Differential Spread Spectrum Code Acquisition

Spread spectrum code acquisition methods based on differential correlation are interesting alternatives to conventional non-coherent acquisition. Differential correlation can be seen simply as a correlation between two consecutive outputs of a coherent integrator. A differential acquisition variable is then obtained by averaging these correlation variables which results in an attenuation of any time-uncorrelated (or weakly time-correlated) interference components in a received signal. An existing analysis on the differential methods is mainly numeric or at least approximative in its nature. In this paper, we carry out rigorous analytic performance comparison of differentially coherent and conventional, non-coherent acquisition in terms of probabilities of detection and false alarm. First, we derive an exact probability distribution for the differential method from which we, then, evaluate the needed probabilities. In addition, we give a theoretical discussion about differentially noncoherent code acquisition which provides more reliable detection under residual frequency errors. Finally, we also give numerical examples to illustrate a suitability of the differential methods in Galileo-satellite positioning system

Signaled Step Size for Downlink Power Control of Dedicated Channels in UTRA TDD

This paper discusses downlink inner loop power control of dedicated channels in UTRA TDD. The current UTRA TDD downlink power control is similar to one in UTRA FDD mode, that comprises of closed inner loop and quality based outer loop. However, due to the time division feature and associated fexibility with asymmetry of TDD, the inner loop can not react as fast as in FDD and it is affected by rapid changes in environment. Therefore, the effect of the inner loop algorithm to the performance of UTRA TDD network is studied in this paper. Especially, the use of asymmetric step sizes for “power up” and “power down” commands is evaluated in contrast to the conventional symmetric power adjustment. Since it would be beneficial for the downlink inner loop power control to reach the target SIR as fast as possible, the power control step size based on the difference between the UE measured SIR and target SIR would be the most desirable power adjustment. Since the effectiveness of this type of an algorithm depends on available signaling bandwidth that is used, a study is carried out to find the tradeoff between the signaling bandwidth and related network performance.

EV-t method for parameter estimation in DS-CDMA communications

In this paper a new method named EV-t is introduced for parameter estimation. The parameters of primary interest are the time delay and direction-of-arrival (DOA). The EV-t method depends on signal subspace of array covariance, and also requires a training sequence corresponding to the desired user to be known. Simulations show the EV-t method does not suffer from a large symbol collection bias, and is also an effective method in the higher MAI environment