Localized Mobility Management for SDN-Integrated LTE Backhaul Networks

Small cell (SCell) and Software Define Network (SDN) are two key enablers to meet the evolutional requirements of future telecommunication networks, but still on the initial study stage with lots of challenges faced. In this paper, the problem of mobility management in SDN-integrated LTE (Long Term Evolution) mobile backhaul network is investigated. An 802.1ad double tagging scheme is designed for traffic forwarding between Serving Gateway (S-GW) and SCell with QoS (Quality of Service) differentiation support. In addition, a dynamic localized forwarding scheme is proposed for packet delivery of the ongoing traffic session to facilitate the mobility of UE within a dense SCell network. With this proposal, the data packets of an ongoing session can be forwarded from the source SCell to the target SCell instead of switching the whole forwarding path, which can drastically save the path-switch signalling cost in this SDN network. Numerical results show that compared with traditional path switch policy, more than 50 signalling cost can be reduced, even considering the impact on the forwarding path deletion when session ceases. The performance of data delivery is also analysed, which demonstrates the introduced extra delivery cost is acceptable and even negligible in case of short forwarding chain or large backhaul latency

HARQ in relay-assisted transmission for machine type communications

This letter describes the impact of unknown channel access delay on the timeline of the hybrid automatic repeat request (HARQ) process in the 3rd generation partnership project long term evolution (3GPP LTE) system when a relay node (RN) is used for coverage extension of machine type communication (MTC) devices. A solution is also proposed for the determination of unknown channel access delay when the RN operates in the unlicensed spectrum band. The proposed mechanism is expected to help MTC operation in typical coverage holes areas such as smart meters located in the basement of buildings

Semi-persistent RRC protocol for machine-type communication devices in LTE networks

In this paper, we investigate the design of a radio resource control (RRC) protocol in the framework of long-term evolution (LTE) of the 3rd Generation Partnership Project regarding provision of low cost/complexity and low energy consumption machine-type communication (MTC), which is an enabling technology for the emerging paradigm of the Internet of Things. Due to the nature and envisaged battery-operated long-life operation of MTC devices without human intervention, energy efficiency becomes extremely important. This paper elaborates the state-of-the-art approaches toward addressing the challenge in relation to the low energy consumption operation of MTC devices, and proposes a novel RRC protocol design, namely, semi-persistent RRC state transition (SPRST), where the RRC state transition is no longer triggered by incoming traffic but depends on pre-determined parameters based on the traffic pattern obtained by exploiting the network memory. The proposed RRC protocol can easily co-exist with the legacy RRC protocol in the LTE. The design criterion of SPRST is derived and the signalling procedure is investigated accordingly. Based upon the simulation results, it is shown that the SPRST significantly reduces both the energy consumption and the signalling overhead while at the same time guarantees the quality of service requirements

FBMC system: an insight into doubly dispersive channel impact

It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur

Performance analysis and optimal cooperative cluster size for randomly distributed small cells under cloud RAN

One major advantage of cloud/centralized radio access network is the ease of implementation of multi-cell coordination mechanisms to improve the system spectrum efficiency (SE). Theoretically, large number of cooperative cells lead to a higher SE; however, it may also cause significant delay due to extra channel state information feedback and joint processing computational needs at the cloud data center, which is likely to result in performance degradation. In order to investigate the delay impact on the throughput gains, we divide the network into multiple clusters of cooperative small cells and formulate a throughput optimization problem. We model various delay factors and the sum-rate of the network as a function of cluster size, treating it as the main optimization variable. For our analysis, we consider both base stations' as well as users' geometric locations as random variables for both linear and planar network deployments. The output signal-to-interference-plus-noise ratio and ergodic sum-rate are derived based on the homogenous Poisson point processing model. The sum-rate optimization problem in terms of the cluster size is formulated and solved. Simulation results show that the proposed analytical framework can be utilized to accurately evaluate the performance of practical cloud-based small cell networks employing clustered cooperation

Opportunistic spectrum access in support of ultra-reliable and low-latency communications

This paper addresses the problem of opportunistic spectrum access in support of mission-critical ultra-reliable and low latency communications (URLLC). Considering the ability of supporting short packet transmissions in URLLC scenarios, a new capacity metric in finite blocklength regime is introduced as the traditional performance metrics such as ergodic capacity and outage capacity are no longer applicable. We focus on an opportunistic spectrum access system in which the secondary user (SU) opportunistically occupies the frequency resources of the primary user (PU) and transmits reliable short packets to its destination. An achievable rate maximization problem is then formulated for the SU in supporting URLLC services, subject to a probabilistic received-power constraint at the PU receiver and imperfect channel knowledge of the SU-PU link. To tackle this problem, an optimal power allocation policy is proposed. Closed-form expressions are then derived for the maximum achievable rate in finite blocklength regime, the approximate transmission rate at high signal-to-noise ratios (SNRs) and the optimal average power. Numerical results validate the accuracy of the proposed closed-form expressions and further reveal the impact of channel estimation error, block error probability, finite blocklength and received-power constraint

On the performance of multi-packet HARQ protocols in NOMA systems

In this paper, we investigate the throughput performance of single-packet and multi-packet hybrid-automatic repeat request (HARQ) with blanking for downlink non-orthogonal multiple access (NOMA) systems. While conventional single-packet HARQ achieves high throughput at the expense of high latency, multi-packet HARQ, where several data packets are sent in the same channel block, can achieve high throughput with low latency. Previous works have shown that multi-packet HARQ outperforms single-packet HARQ in orthogonal multiple access (OMA) systems, especially in the moderate to high signal-to-noise ratio regime. This work amalgamates multi-packet HARQ with NOMA to achieve higher throughput than the conventional single-packet HARQ and OMA, which has been adopted in the legacy mobile networks. We conduct theoretical analysis for the throughput per user and also investigate the optimization of the power and rate allocations of the packets, in order to maximize the weighted-sum throughput. It is demonstrated that the gain of multi-packet HARQ over the single-packet HARQ in NOMA systems is reduced compared to that obtained in OMA systems due to inter-user interference. It is also shown that NOMA-HARQ cannot achieve any throughput gain with respect to OMA-HARQ when the error propagation rate of the NOMA detector is above a certain threshold

Throughput Analysis and User Barring Design for Uplink NOMA-Enabled Random Access

Being able to accommodate multiple simultaneous transmissions on a single channel, non-orthogonal multiple access (NOMA) appears as an attractive solution to support massive machine type communication (mMTC) that faces a massive number of devices competing to access the limited number of shared radio resources. In this paper, we first analytically study the throughput performance of NOMA-based random access (RA), namely NOMA-RA. We show that while increasing the number of power levels in NOMA-RA leads to a further gain in maximum throughput, the growth of throughput gain is slower than linear. This is due to the higher-power dominance characteristic in power-domain NOMA known in the literature. We explicitly quantify the throughput gain for the very first time in this paper. With our analytical model, we verify the performance advantage of the proposed NOMA-RA scheme by comparing with the baseline multi-channel slotted ALOHA (MS-ALOHA), with and without capture effect. Despite the higher-power dominance effect, the maximum throughput of NOMA-RA with four power levels achieves over three times that of the MS-ALOHA. However, our analytical results also reveal the sensitivity of load on the throughput of NOMA-RA. To cope with the potential bursty traffic in mMTC scenarios, we propose adaptive load regulation through a practical user barring algorithm. By estimating the current load based on the observable channel feedback, the algorithm adaptively controls user access to maintain the optimal loading of channels to achieve maximum throughput. When the proposed user barring algorithm is applied, simulations demonstrate that the instantaneous throughput of NOMA-RA always remains close to the maximum throughput confirming the effectiveness of our load regulation

Opportunistic spectrum sharing for D2D-based URLLC

A device-to-device (D2D) ultra-reliable low latency communications network is investigated in this paper. Specifically, a D2D transmitter opportunistically accesses the radio resource provided by a cellular network and directly transmits short packets to its destination. A novel performance metric is adopted for finite block-length code. We quantify the maximum achievable rate for the D2D network, subject to a probabilistic interference power constraint based on imperfect channel state information. First, we perform a convexity analysis that reveals that the finite block-length rate for the D2D pair in short-packet transmission is not always concave. To address this issue, we propose two effective resource allocation schemes using the successive convex approximation based iterative algorithm. To gain more insights, we exploit the monotonicity of the average finite block-length rate. By capitalizing on this property, an optimal power control policy is proposed, followed by closed-form expressions and approximations for the optimal average power and the maximum achievable average rate in the finite block-length regime. Numerical results are provided to confirm the effectiveness of the proposed resource allocation schemes and validate the accuracy of the derived theoretical results

Link-level performance characterisation and optimisation of UTRA FDD downlink.

In this thesis, we investigate the frequency division duplex (FDD) mode of the downlink of UMTS terrestrial radio access (UTRA) focusing on the signal to interference ratio (SIR) estimation for the closed loop power control (CLPC), diversity exploitation in both spatial and temporal domains and the suppression of multi-access interference that is encountered in handover regions, with the aid of a calibrated link-level simulator. Firstly, SIR estimation methods are studied for single and two-antenna transmissions and it is shown that when the common pilot channel (CPICH) is available, SIR could be estimated on that and related to the SIR for the dedicated physical channel (DPCH) through a simple relation. This way, a reduction in the overhead of the slot formats specified by the 3GPP, could be obtained. Secondly, factors influencing the handover performance such as the multipath fading correlation between radio channels of the two links, limited number of Rake fingers in a UE and imperfect channel estimation that cannot be modeled adequately at the system-level are investigated via link-level simulations. It is shown that the geometry factor has an influence on the handover performance and exhibits a threshold value (which depends on the correlation of the two links) above which the capacity starts degrading. The variation of the handover gain with the CLPC step-size, space-time transmit diversity (STTD) and receive antenna diversity is also quantified. Thirdly, blind interference suppression techniques are studied for the rejection of multi-access interference in handover regions. It is shown that the CLPC acts as an effective solution to the mismatch problem associated with the minimum output energy (MOE) detector. Furthermore, two methods are proposed for increasing the convergence speed of the MOE detector. Finally, chip-interleaved induced time diversity is investigated for multimedia broadcast / multicast services (MBMS) in UMTS, as a method of enhancing the downlink capacity. It is shown that the chip block interleaving with a block length of half the spreading factor provides similar diversity gain (by using only one transmit antenna) as that provided by STTD, but at the cost of an additional delay that is equal to the interleaving depth. Simulation results are presented for both the terrestrial and satellite modes of MBMS delivery for a range of mobile velocities