Esa Malkamaki

Coded diversity on block-fading channels

This paper considers coded diversity schemes over block-fading Rician channels using random coding techniques. Two random coding upper bounds on the error probability of block codes are derived: a new bound and a simpler but looser bound assuming binary input distribution. Also, a new lower bound for any block code is derived using the strong converse to channel coding theorem. The lower bound shows that the new random coding upper bound is quite tight. Furthermore, it is shown that the maximum achievable diversity order in a block-fading channel with finite interleaving depends not only on the number of subchannels L, but also on the code rate R and that the performance can only marginally be improved by increasing the block length of the code. The random coding upper bound and the lower bound are shown to converge to the capacity outage for large channel block lengths N, demonstrating that the capacity outage can be used for estimating the error probability of coded diversity schemes.

Evaluating the performance of convolutional codes over block fading channels

This correspondence considers union upper bound techniques for error control codes with limited interleaving over block fading Rician channels. A modified bounding technique is presented that relies on limiting the conditional union bound before averaging over the fading process. This technique, although analytically not very attractive, provides tight and hence useful numerical results.

Performance of truncated type-II hybrid ARQ schemes with noisy feedback over block fading channels

This paper considers truncated type-II hybrid automatic repeat-request (ARQ) schemes with noisy feedback over block fading channels. With these ARQ techniques, the number of retransmissions is limited, and, similar to forward error correction (FEC), error-free delivery of data packets cannot be guaranteed. Bounds on the average number of transmissions, the average coding rate as well as the reliability of the schemes are derived using random coding techniques, and the performance is compared with FEC. The random coding bounds reveal the achievable performance with block codes and maximum-likelihood soft-decision decoding. Union upper bounds and simulation results show that over block fading channels, these bounds can be closely approached with simple terminated convolutional codes and soft-decision Viterbi decoding. Truncated type-II hybrid ARQ and the corresponding FEC schemes have the same probability of packet erasure; however, the truncated ARQ schemes offer a trade-off between the average coding rate and the probability of undetected error. Truncated ARQ schemes have significantly higher average coding rates than FEC at high and medium signal-to-noise ratio even with noisy feedback. Truncated ARQ can be viewed as adaptive FEC that adapts to the instantaneous channel conditions.

Principle and Performance of Semi-Persistent Scheduling for VoIP in LTE System

This paper presents an effective scheduling scheme called semi-persistent scheduling for VoIP service in LTE system. The main challenges of effectively supporting VoIP service in LTE system are 1) the tight delay requirement combined with the frequent arrival of small packets of VoIP traffic and 2) the scarcity of radio resources along with control channel restriction in LTE system. Simulation results show that semi-persistent scheduling can support high system capacity while at the same time guaranteeing the QoS requirements such as packet delay and packet loss rate of VoIP. Furthermore, semi- persistent scheduling requires less control signaling overhead which is very important for efficient resources utilization in a practical system.

VOIP over HSPA with 3GPP Release 7

This paper presents air interface capacity simulations for VoIP (voice-over-IP) over 3GPP Release 7 high speed packet access (HSPA) networks. The results show that 3GPP HSPA is able to provide VoIP spectral efficiency which is higher than the spectral efficiency for circuit switched voice calls with the same end-to-end quality. The high VoIP efficiency can be attributed to the packet optimization features in 3GPP Release 5, 6 and 7 specifications, to the advanced mobile receiver algorithms and to the VoIP optimized radio network algorithms. The studies also show that HSPA mobility solutions fulfil VoIP requirements with synchronous handover even if HSDPA does not use soft handover

Performance of hybrid ARQ techniques for WCDMA high data rates

Hybrid ARQ is being considered as a potential method for improving the performance of WCDMA in UMTS. We compare different hybrid ARQ techniques, namely the incremental redundancy type II hybrid ARQ schemes and type I hybrid ARQ schemes with and without soft combining. The emphasis is at high data rates and downlink shared channel (DSCH). Both link and system simulations are used for comparison. The hybrid ARQ schemes are shown to achieve higher throughput and capacity than the conventional ARQ schemes currently specified in the 3GPP WCDMA standard. Also, the combining of packets can cut the tail of the delay distribution which reduces the required maximum number of transmissions. However, the complexity increase due to physical layer buffering in the mobile station is too high if the round trip delay is large.

Coded diversity schemes on block fading Rayleigh channels

This paper considers coded diversity schemes on block fading Rayleigh channels. Based on random coding techniques we analyze the performance of binary block codes on such channels. New upper and lower bounds to the error probability are derived. The new upper bound, that is tighter than previously known results, reveals that the maximum diversity order achieved in a block fading channel with finite interleaving is dictated not only by the number of diversity channels L but also by the code rate R, and that the performance can be only marginally improved by increasing the block length of the code. Furthermore, it was found that low rate codes can effectively exploit the available diversity. For diversity order of L, codes of rate 1/L are in particular advantageous. The gains over conventional diversity schemes are shown to be significant (3-6 dB). Examples of systems that our model can be used for are the GSM or PCS1900, and the ATDMA proposal for UMTS. These systems employ slow frequency hopping TDMA.

On LTE performance trade-off between connected and idle states with always-on type applications

In cellular networks it is envisioned an explosion of diverse data applications running in smart phones, which could increase significantly not only user plane but also control plane load in the network. Smart phones and their always-on applications introduce several challenges: From the network perspective, an increased amount of UEs/applications can increase the signaling load due to frequent state transitions and handover signaling. From the UE perspective, challenges of power consumption are evident, since UE would increasingly be in connected state. In this article we study the trade-off between releasing the UE into idle state vs. keeping the UE in connected state, in a LTE system. The results indicate that optimum performance can be achieved using UE specific RRC release timer and DRX configurations by taking advantage of traffic characteristics and UE mobility.

Rate 1/n convolutional codes with interleaving depth of n over a block fading Rician channel

Rate 1/n convolutional codes with interleaving depth of n are analysed in a frequency non-selective block fading Rician channel. The channel is assumed to be constant during the transmission of a block and independent from block to block. A generalised transfer function, T(D/sub 1/,...,D/sub n/,N), is used for calculation of union transfer function upper bounds on the average bit and block error probabilities. Numerical results indicate that the bounds are relatively tight (1-3 dB) and clearly show that at most a diversity order of n is achieved. The component distance product is shown to be an important parameter for code design.

A method for combining radio link simulations and system simulations for a slow frequency hopped cellular system

To assess the performance of an advanced mobile radio access system, it is important to make use of suitable simulation tools in order to evaluate the impact on the system of the different control and adaptation mechanisms. In order to have accurate results from such system simulations, the radio link performance has to be modelled. Separate radio link simulations are used to give the performance results. A two step look-up table approach is presented for the combining of the radio link simulations with the system simulations. The look-up tables allow an accurate modelling of the transport chain in the system simulations.<<ETX>>