Offloading traffic to small cells is one of the key enablers in achieving high peak data rates in a heterogeneous cellular network deployment. In this paper, we introduce and evaluate a solution to significantly speed up the small cell access in LTE or NR based on UE performing additional small cell measurements in idle state. These additional measurements naturally have a cost as additional energy consumption in the UE, but enable much faster small cell setup when there is data. The conventional wisdom has been to minimize the amount of measurements in the idle state to keep the UE battery life as long as possible. However, our results show that by leveraging the substantially better energy efficiency of data transmission in a small cell, a net positive effect can be achieved in a typical scenario. The performance gains are compelling: We observe user perceived throughput up to 5-10 times higher, while still maintaining lower average UE energy consumption.

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.

In order to further improve the packet performance in the UMTS FDD system, uplink dedicated physical control channel (DPCCH) gating as a scheme is proposed in 3GPP under the work item "continuous connectivity for packet data users". In this paper, the uplink DPCCH gating concept is described and analyzed on both a qualitative and a quantitative level. And the system performance of different gating patterns used in the scheme was investigated by analytical prediction and system level simulations with different channel profiles. As shown, the selection of the gating pattern has a significant influence on the system performance, which is correlated with the uplink data transmission activity and the uplink power control. This contributes to a better understanding of the effects involved with uplink DPCCH gating where the biggest potential for performance optimizations can be found. In summary, the scheme of the uplink DPCCH gating is promising to improve the packet performance.

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.

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

In this paper, the system performance of VoIP on HSUPA, which is investigated by the semi-analytical prediction and the system level simulations, was studied and presented. The semi-analytical results show the capacity gain of VoIP over HSUPA than 12.2kbps on DCH in Rel'99. Further, the aforementioned prediction shows the consistency with system level simulation results in principle. Otherwise, the uplink capacity of VoIP over HSUPA with non-scheduled algorithm is mainly dependent on the delay budget and availability of the UE power, which is indicated by the results. HARQ and soft handover can be expected to lower the required UE power and thus increase the capacity. Due to the time sensitivity of VoIP service, a compromise between the maximum number of HARQ retransmissions and the delay budget can be considered to optimize the capacity of VoIP on HSUPA.

In this paper, link performance aspects of the high speed uplink packet access (HSUPA), evolution of the WCDMA/UTRA-FDD standard, are investigated. The main focus is on the impact of the transmit time interval (TTI) on the overall system performance. Different aspects should be taken into account when choosing the TTI to be used. The simulation results presented here could give system designers a tool for the clarification of the problem

This paper deals with the link performance of the enhanced uplink dedicated channel (E-DCH), a new concept currently studied in 3GPP for introduction in the WCDMA/UTRA-FDD standard. A key feature of E-DCH is the physical/MAC layer retransmission, employing soft combining of different versions of the same packet to improve the performance of the link. In order to evaluate the possible gain from this new feature, extensive link-level simulations are needed, which take into account even the effect of the needed side signaling on the overall performance. This paper presents results for some interesting cases, considering in particular the situation of a user in soft handover (SHO).

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.

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.

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.

This paper considers type-II hybrid ARQ schemes with convolutional codes over block fading Rayleigh channels with limited interleaving. Examples of systems that our results can be used for are GSM (or PCS1900) and TDMA based proposals for UMTS. These systems employ slow frequency hopping TDMA, and typically operate over fading channels. Analytical upper bounds on packet and decoded block error probabilities are used to derive lower bounds on throughput. It is shown that over a block fading channel, the throughput with limited interleaving is higher than with ideal interleaving.

Burst-level ARQ, a new error protection scheme for speech transmission, is based on ARE (automatic repeat request) which is used on burst level, i.e., only the erroneous bursts are repeated. It is more flexible than a conventional error protection based on forward error correction (FEC) because the redundancy is sent only when required. Furthermore, with a limited number of retransmissions, it provides a low delay. The performance of the burst-level ARQ is studied by computer simulations in an indoor environment and compared with conventional FEC schemes using convolutional codes and interleaving. The cellular capacity of both schemes is calculated taking into account the required carrier capacity (i.e., the number of slots per TDMA frame) as web as the frequency reuse efficiency (i.e., the robustness to co-channel interference). The burst level ARQ is shown to be a good solution when low delay and high performance is required.>

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.>