Forward Access Channel Research Articles

Measuring and Understanding RRC State Machine Optimization in Light of Recent Advancements

Broadband mobile networks utilize a radio resource control (RRC) state machine to allocate scarce radio resources. Current implementations introduce high latencies and cross-layer degradation. Recently, the RRC enhancements, continuous packet connectivity (CPC), and the enhanced forward access channel (Enhanced FACH), have emerged in UMTS. We measure the availability and performance of these enhancements on a network serving a market with a population in the millions. We demonstrate that these enhancements offer significant reductions in latency, mobile device energy consumption, and improved end user experience. We develop new over-the-air measurements that resolve existing limitations in measuring RRC parameters. We find CPC provides significant benefits with minimal resource costs, prompting us to rethink past optimization strategies. We examine the cross-layer performance of CPC and Enhanced FACH, concluding that CPC provides reductions in mobile device energy consumption for many applications. While the performance increase of HS-FACH is substantial, cross-layer performance is limited by the legacy uplink random access channel (RACH), and we conclude full support of Enhanced FACH is necessary to benefit most applications. Given that UMTS growth will exceed LTE for several more years and the greater worldwide deployment of UMTS, our quantitative results should be of great interest to network operators adding capacity to these networks. Finally, these results provide new insights for application developers wishing to optimize performance with these RRC enhancements.

Enhanced radio resource management algorithms for efficient MBMS service provision in UTRAN

As currently specified by 3GPP, Multimedia Broadcast Multicast Service (MBMS) bearer services can be provided within a cell either by Point-to-Point (P-t-P) or Point-to-Multipoint (P-t-M) transmission mode, but not both at the same time. If P-t-P transmission mode is selected for a cell, one Dedicated Channel (DCH) is established for each user within the cell that joined the MBMS service. Otherwise, if P-t-M transmission mode is selected, one Forward Access Channel (FACH) is established covering the whole cell’s area and commonly shared by all the UEs within. In this paper, we highlight the inefficiencies that can be caused with the aforementioned approach and introduce the “Dual Transmission mode cell” in which P-t-P and P-t-M transmissions (i.e. multiple DCHs and FACH) are allowed to coexist within the same cell. Hence, we propose a new radio resource allocation algorithm and solution to address them. Our proposed algorithm considers the instantaneous distribution and movement of the users within the cell and dynamically decides which users will use FACH and which DCH, in such a way that the requested Quality of Service (QoS) is supported with the least amount of transmission power (i.e. capacity) consumption. Moreover, with the “Dual Transmission mode cell”, new types of intra-cell handovers are introduced which we also analyse and propose a new handover algorithm to address them. The performance evaluation carried out showed that our proposed “Dual Transmission mode cell” approach, provides considerable gains, as well as outperforming all other related approaches, such as “UE Counting”, “Power Counting”, “Rate Splitting”, and “FACH with dynamic power setting”, in terms of capacity and link performance efficiency.

Broadcast and multicast transmission over HSDPA

In this paper, we describe the novel concept of broadcast and multicast (BCMC) transmission over high speed downlink packet access (HSDPA), a shared high-speed packet data channel on the downlink defined in the Universal Mobile Telecommunications System (UMTS) standard. We show that the unique features of HSDPA such as link adaptation, channel-sensitive scheduling, and hybrid automatic repeat request (HARQ) can be used to provide performance gains over conventional multimedia broadcast multicast service (MBMS) transmission on the forward access channel (FACH) channel. We address various aspects of system design and performance in the design of a BCMC system over HSDPA, and present a detailed performance analysis using system level simulations. Some of the main objectives of our BCMC design are to enable broadcast and multicast services on HSDPA networks without requiring significant changes to the HSDPA standard in 3rd Generation Partnership Project (3GPP), and to ensure that the solution is backward-compatible with Release 5 HSDPA mobile devices.

Packet service in UMTS: delay-throughput performance of the downlink shared channel

The Universal Mobile Telecommunications System, wide band code-division multiple access (W-CDMA) radio interface is characterized by great flexibility and a variety of different physical and logical channel types: for example, on the downlink the dedicated channels (DCH) offers circuit switching, the downlink shared channel (DSCH) and forward access channel use packet switching, the former with closed loop power control. Furthermore, several user rates and protections are possible, by choosing suitable parameters, such as spreading factors (SFs), code rates and automatic repeat request (ARQ) schemes. In this paper we present the results, obtained by a detailed simulation, about the effect of several parameters and system alternatives on the capacity of the downlink segment of the W-CDMA interface with packet service. In particular, we investigate the effect of the SF, the code rate, the ARQ and the power control on the DSCH capacity and delay-throughput performance.