Henrik Lundqvist

Adaptive end-to-end FEC for improving TCP performance over wireless links

TCP is a reliable transport protocol that has been tuned to perform well in networks where packet losses occur mostly because of congestion. However, wireless networks are different: TCP responds both to congestion-based and error-based losses by invoking a congestion control algorithm and reducing the sending rate, resulting in degraded end-to-end performance for wireless systems. We investigate a new end-to- end approach for improving TCP performance over lossy links by using adaptive, end-to-end forward error correction (FEC) for recovering losses and consequently avoiding the TCP back-off behaviour. Of course there is a clear trade-off between the capacity consumed by FEC and the gain achieved in the overall throughput. An adaptive algorithm is needed to calculate the optimum ratio of redundancy given the state of the connection. The sender uses feedback information from the receiver to dynamically tune the FEC parameters. Through simulations we evaluate the performance of TCP with end-to-end FEC in mixed wired and wireless networks. The simulation results show in different scenarios that the throughput can be significantly improved by adding end-to-end FEC to TCP. However, compared to other improved TCP variants such as Westwood+ the performance is not improved, hence a direct modification of TCP congestion control appears to be more efficient than adding end-to-end FEC.

TCP with end-to-end FEC

In this paper we investigate the effects of combining end-to-end forward error correction (FEC) with TCP. FEC reduces the number of retransmissions and results in different congestion control behaviour, effectively running the network at a higher load. The interaction between TCP and FEC is discussed and the conclusion is that the FEC has to be adaptive to work efficiently. Unless the block length of the error correction is adapted to the window size of TCP, deadlocks can occur. A simple adaptation algorithm is proposed and the performance is evaluated by simulation. It is found that in certain scenarios the performance can be increased significantly, in particular for large delay and when losses are caused by noise.

On error-correction coding for CDMA PON

Optical-code-division multiple access (OCDMA) has been investigated as a multiple-access technique for a long time, but so far, it has not reached any practical success. We investigate the performance of low-complexity OCDMA systems with a realistic model of noise and interference; the main limitation of the system is beat noise. To improve the performance, we consider forward-error correction (FEC) and soft decoding using standard error-correcting codes. The achievable error rates are evaluated using simulations and show significant improvement when FEC is used. The results also show that frequency-hopping systems perform better than temporally coded systems when beat noise is taken into account.

Distributed Self-Optimization of Handover for the Long Term Evolution

The 3GPP Long Term Evolution (LTE) is defining the next generation radio access network which introduces advanced service capabilities in base stations. Consequently, self-management is seen as an enabling technique for the deployment of LTE. This paper discusses handover optimization options for base stations and evaluates one possible approach of distributed self-optimization. After a review of the key aspects related to handover optimization, a self-optimization technique for handover based on trial-and-error is presented. The interference between neighboring nodes, a typical problem of distributed systems, is analyzed in more detail and a technique to cope with it is presented. Simulation results show that the control algorithm can achieve the expected optimal configuration through iterative steps and the effect of interfering neighboring nodes can be mitigated at the expense of a longer optimization time.

Smart Direct-LTE communication: An energy saving perspective

Direct-LTE communication underlying a cellular infrastructure, or more commonly known as device to device (D2D), is discussed in this paper. When enabling D2D communication in the system, one can see several benefits compared to the conventional infrastructure based communication, such as improved energy efficiency, increased overall system throughput and decreased traffic load in the network. The aim of this paper is to give an energy efficiency perspective of D2D communication to assist all major mobile stakeholders to perceive the benefits when facilitating D2D communication in the network. This paper is tutorial in nature, initially elaborating on the fundamental concept surrounding D2D communication towards technical perspective, business opportunities and open challenges when considering deployment. Furthermore, a simulation study of a typical D2D use case is carried out that includes the energy efficiency perspective; we use 3GPP Long Term Evolution Advanced (LTE-A) as a baseline technology and candidate for launching D2D communications.

User-assisted coverage and interference optimization for broadband femtocells

We present ways for user-assisted coverage configuration and interference optimization. The femtocell coverage is measured in a user-assisted site survey, followed by an automatized evaluation and femtocell configuration adjustment. To achieve this, the user only needs his mobile phone for interaction. Existing, commercial technology only offers measurement of the radio environment and a visualization of the respective results. We describe how measurements of at least two measurement series at different power levels along an identical path can be used to find a good configuration in an automatized manner. It is described how measurement sequences can be aligned to make them comparable to each other.

Edge-based differentiated services

Network quality of service is traditionally thought to be provided by a combination of scheduling in the network nodes to enforce a capacity sharing policy and traffic controls to prevent congestion that could annihilate that policy. The work presented herein is instead based on an end-to-end argument: A capacity sharing policy is enforced by traffic controls in the hosts at the edges of the network, without any scheduling support in the network. Our proposal is to add a feed-forward control at the transport layer to provide a service that is better suited to conversational and streaming applications than the batch-oriented transfer mode provided by TCP. The paper presents the control and its evaluation: We compare the sharing of capacity between traffic classes and study the loss rate seen by admitted streams. The outcome is that the new control adds a distinctly different service to the service offered by TCP for the Internet.

A quantitative analysis of the throughput gains and the energy efficiency of multi-radio transmission diversity in dense access networks

Densification of mobile network infrastructure and integration of multiple radio access technologies are important approaches to support the increasing demand for mobile data traffic and to reduce energy consumption in future 5G networks. In this paper, the benefits of multi-radio transmission diversity (MRTD) are investigated by modelling the radio access link throughputs as uniform- and Rayleigh-distributed random variables and evaluating different user schedulers and resource allocation strategies. We examine different strategies for the allocation of radio accesses to individual users ranging from independent utilisation of the radio accesses to MRTD-enabled schemes. The schemes are compared by considering the statistics of the system throughput and energy consumption of the mobile devices. It is shown that MRTD can increase the throughput significantly through two types of diversity gain: Firstly by having multiple radio accesses to choose from for each user and secondly by having more available users to choose from for each radio access. The increased throughput also helps to reduce the energy consumption per bit, but this comes at a cost of increased energy consumption for channel measurement and reporting.

Fast RTP Retransmission for IPTV - Implementation and Evaluation

With the deployment of IPTV reliability for multicast is becoming an important research topic again. Even though it has been intensively investigated before, there is now an understanding of the deployment scenario and the application requirements that allows solutions to be evaluated in detail. We describe how to design a fast retransmission cache based on recent extensions of RTP. We have implemented a prototype intended for deployment in an access node and explain the necessary trade-offs in the design. The paper also contains a performance evaluation which shows the efficiency of the retransmission functionality to handle losses and its performance in congested networks.

Single-service quality differentiation

This paper proposes a scheme for quality of service differentiation for single-service networks that is based on the use of two separate forms of traffic control at the transport layer: Streams are controlled by means of probe-based admission control and elastic flows are controlled by TCP. The controls allow separation of traffic into two distinct service classes. The stream class is designed to provide a consistent quality for interactive audiovisual communication, as favored by human perception. It is responsive to load variations as an aggregate through blocking of sessions, while TCP is responsive on the flow level. Streams can be isolated against disturbances from probes and TCP flows by means of error-control coding. We show that the two traffic controls can coexist without starvation, and the proposed scheme might thus provide a first step towards differentiated services end-to-end.