Hans Hannu

Evaluation of CRTP performance over cellular radio links

To make mobile IP telephony over cellular radio systems an economically viable alternative to circuit-switched voice, it is an absolute requirement that the 40-octet IP/UDP/RTP headers on IP telephony packets be reduced in size to conserve bandwidth and radio spectrum. We evaluate the performance of the default header compression scheme for IP/UDP/RTP, CRTP (RFC-2508), over links built on cellular radio access technology. We find that CRTP does not perform adequately over such links, and suggest that a more robust header compression scheme must be developed to make IP telephony over cellular economically viable.

Wireless real-time IP services enabled by header compression

The world of telecommunications is currently going through a shift of paradigm from circuit switched, connection oriented information transfer towards packet switched, connection-less transfer. For application independence and to decrease costs for transport and switching it is attractive to go IP all the way over the air interface to the end user equipment, i.e., to not terminate the IP protocols before the air interface. A major reason to avoid using voice over IP over the air interface has, up to now, been the relatively large overhead imposed by the IP/UDP/RTP headers of voice packets. This paper presents a novel header compression scheme, ROCCO, that can compress the large headers to a minimum of one octet and is robust against the errors imposed by cellular links. Its performance is excellent both in terms of robustness and compression efficiency. Moreover, system capacity simulations are presented, which show that ROCCO gives significantly higher system capacity than the other current header compression candidate, CRTP. Finally it is argued that with ROCCO voice over IP over wireless becomes feasible from a spectrum-efficiency point of view.

Efficient transport of voice over IP over cellular links

Internet and cellular technologies are merging to decrease transport costs and enable IP-based applications to hundreds of millions of cellular users. Real time voice services will continue to be dominant in future cellular systems and to reduce system costs it is desirable to base all services, including voice, on IP. However, the radio spectrum must be efficiently used to provide mass-market services at reasonable prices, but Internet protocol headers are large in size. Moreover, data discarding policies are poorly suited to the error-proneness of cellular links. Protocol overhead for IP-based voice services can be reduced by compressing headers, e.g. with the compressed real time protocol (CRTP). CRTP, however, does not perform well over cellular links since it is not robust in the face of errors. ROCCO, a header compression scheme suitable for cellular systems, delivers more packets to the user than CRTP at realistic error rates with a better average compression ratio. Voice services in cellular systems should also be able to use damaged speech data. This can be done using the UDP Lite protocol which provides a more flexible checksumming policy that enables delivery of data possibly usable to the application. This paper shows that CRTP/UDP fails to deliver sufficient service quality at the error rates of a cost-efficient cellular system and that ROCCO combined with UDP Lite can provide an IP-based voice service over such cellular systems.

Improving SigComp performance through extended operations

This paper demonstrates the efficiency gains achievable for the compression scheme SigComp using extended operations where information from previously sent and received messages is used. The calculations are performed for a call setup using SIP in a typical 3GPP scenario. It is estimated that the transmission time over the air interface can be reduced by approximately 2/3. Also, the performance in terms of compression efficiency can be doubled, compared to using message by message compression with SigComp.

End-to-end performance of WCDMA enhanced uplink

In this paper we study the end-to-end performance of the enhanced uplink of WCDMA. We present results for latency and TCP performance on both uplink and downlink when using the enhanced uplink. The results show that the enhanced uplink can significantly improve the end-to-end performance of both for up- and downlink oriented traffic when compared to the uplink provided by 3GPP R5. The expected performance depends strongly on the configuration of the enhanced uplink, especially on the HARQ operating point.

Public Safety Communication Using Commercial Cellular Technology

We propose a concept for public safety communication realized with IMS (IP multimedia subsystem), the cellular standards of 3GPP and packet switched transmission. Basing the solution on mainstream cellular technology leverages the economy of scale of todays commercial networks and enables migration of technical solutions and applications. Important requirements of the public safety sector are group communication, low latency, high capacity, security, reliability and interoperability for voice and broadband data services. Our analysis shows that the concept has the technology potential to meet these public safety requirements.

Optimization of Fairness for HTTP Adaptive Streaming with Network Assistance in LTE Mobile Systems

HTTP adaptive streaming is becoming dominant for commercial video streaming services. It is typically the client that chooses the rate based on estimation of the available network bandwidth in order to avoid the client buffer to be underrun or overrun. However, the unfairness among the clients and between the clients and other competing traffic has been identified as one of major issues that lead to degraded user service quality and system capacity. Therefore, this paper proposes a network assisted rate adaptation method for HTTP streaming in the radio access network. The simulation results show that the network rate assistance is able to guarantee a fair share of the network resources. As a result, the system capacity and the user service quality can be improved.

Network assisted rate adaptation for conversational video over LTE, concept and performance evaluation

This work investigates rate adaptation of conversational video in a mobile system using Long Term Evolution, LTE, and where the adaptation is assisted by the radio network. The conventional way to do rate adaptation is through adaptation in the end-points where the transmission rate is selected based on measurements of received packets. This study investigates two network-based algorithms for rate adaptation, a rate fair algorithm that assigns the same rate to all conversational video users in a cell, and a resource fair algorithm that aims to give all users in the cell a fair amount of resources. Both algorithms are combined with delay based scheduling. Both network-based algorithms perform excellently. The delay stays low even when the resource utilization is close to 100%, and the video rate is adapted to the system load. As could be expected, the average user rates are higher with the resource fair algorithm. An end-point based adaptation algorithm is investigated as well, but it cannot keep a low delay at high load.