Kolio Ivanov

Performance evaluation of IEEE802.16 WiMax with fixed and mobile subscribers in tight reuse

WiMax broadband MAN based on the IEEE 802.16d/e standard supports mobile as well as fixed wireless access services. The underlying subscriber data links are characterised by totally different radio conditions such as propagation, interference rejection capability, terminal antenna gain, pattern and height. This leads to a significant coverage mismatch, different user throughput, system capacity and spectrum efficiency. In this paper, the basic performance of mobile and fixed subscribers has been thoroughly analysed for homogeneous hexagonal 3.5 GHz cellular deployments of an OFDM-based WiMax system depending on cell size, frequency reuse and offered traffic load. Network level simulation results on user FTP-application throughput, channel load, modulation and coding scheme utilisation and packet call blocking have been presented for cell radius of 300, 1000 and 2000 m in tight 1 × 1 and 1 × 3 frequency reuse, respectively. The future performance enhancements from optional features as Block Turbo Coding, downlink Power Control, scheduling schemes, sub-channelling in scalable OFDMA and advanced antenna technology have been evaluated and simulation results provided.

Frequency hopping spectral capacity enhancement of cellular networks

In the highly competitive mobile radio market the resource system spectrum is often shared between at least two system operators while the capacity demands and quality requirements are dramatically increasing. Wideband random frequency hopping (FH) in digital F/TDMA systems like GSM and its derivatives is a method of expanding the bandwidth used by a traffic channel, thereby creating frequency and interference diversity effects. In this paper the diversity effects of random FH are analysed by means of combined link and system level simulations of the GSM full rate speech channel embedded in different network simulation environments in different network configurations. The results indicate that even without power control the use of random FH with discontinuous transmission (DTX) provides both spectral capacity enhancement and improved quality for slow-moving mobiles in particular. We show that with a total of 24 frequencies available for traffic a fractionally loaded 1/3 reuse scheme yields a spectral capacity increase of 84% compared with a non-hopping 4/12 reuse scheme at the same speech quality level.

Performance analysis of IEEE802.16 based cellular MAN with OFDM-256 in mobile scenarios

The recent IEEE802.16d/e standardization initiative for wireless metropolitan area networking (MAN) aims at portable and mobile broadband wireless access (BWA) in cellular deployments as well as conventional fixed residential high throughput access (e.g. wireless DSL) and feeding applications such as IEEE802.11 WLAN hotspot backhaul. This paper focuses on the basic IEEE802.16d/e performance presenting end-to-end application throughput, capacity and spectrum efficiency figures for pure mobile scenarios. Detailed link level and system level simulations have been performed in interference limited cellular environment for tight 1x1 and 1x3 frequency reuse showing very promising results on 3.5 MHz OFDM channels (256 sub-carriers) in the 3.5 GHz band. The dependency of the application throughput, channel utilization and coding scheme distribution on the system load has been thoroughly analyzed. It is shown that admission control functionality is mandatory for a system in 1x1 reuse to avoid overload and packet call blocking conditions, whereas 1x3 reuse works properly over the entire system load range.

Performance analysis of a GERAN switched beam system by simulations and measurements

Switched beam (SB) technology is an appropriate method for boosting GSM/EDGE radio access network (GERAN) capacity especially in hot spots or cell deployments, where the installation of additional sites and new antennas is not possible. A SB solution with four 30 degree sub-sectors is presented and the potential capacity gain in uplink and downlink is evaluated by simulations and drive tests. A performance comparison with the upcoming single antenna interference cancellation (SAIC) feature is given for the downlink. Finally, it is shown that SB and SAIC provide an additive quality and capacity gain.

Link quality control benefits from a combined incremental redundancy and link adaptation in EDGE networks

A performance analysis of link quality control (LQC), comprising incremental redundancy (IR) and link adaptation (LA) in EDGE networks has been provided. Both simulated and real system measurement results demonstrate the superiority of the proposed combined IR+LA strategy over pure IR. LLC and TCP/IP protocol stack simulations show that a pure IR strategy causes upper layer protocol implications as well as frequent TCP retransmissions resulting in considerable throughput degradations especially under bad C/I conditions. In this case, a combined IR+LA strategy reduces the TCP/IP packet delay and avoids upper layer timer expiries by switching to a more robust coding scheme. Hence, under bad radio conditions, with IR+LA the application throughput is preserved at an optimum level.

Advanced quality of service strategies for GERAN mobile radio networks

Customer demand for wireless data services is rapidly increasing. The introduction of GPRS, EDGE and UMTS providing high bit rate radio bearer, however, is not the complete response for satisfying the demands of these new high quality services. An advanced quality of service QoS management is necessary to handle the characteristic requirements of both different service types and user expectations. A new QoS strategy is proposed and analyzed comprising 3GPP QoS parameters along with operators specific weighting factors to define the appropriate QoS priority of each service type and user profile. Admission control as well as a deterministic up-and downgrading strategy are applied to ensure a minimum grade of service for low-priority applications. Furthermore, delay time sensitive services and premium users are granted a full bandwidth. Simulation results are provided to qualify the behavior of the proposed QoS strategy under different packet data load conditions. Especially in highly loaded and even overloaded GERAN networks the introduction of QoS provides significant benefits for the end user and offers powerful means to increase the service revenues according to the charging policy adopted by the network operator. The introduction of an appropriate QoS strategy is the prerequisite for an overlay deployment strategy of GSM/EDGE and UMTS.

Performance analysis of dynamic TDM-transport for GSM voice and GPRS/EDGE packet data services

Todays GSM and GPRS mobile networks are based on static 16 kbps terrestrial transport on the Abis interface using E1/T1 lines. For the introduction of the high data rate GPRS coding schemes such as CS4 with up to 20 kbps, EDGE with up to 59.2 kbps and high quality wideband adaptive multirate voice codecs with up to 23.85 kbps the terrestrial Abis capacity per air interface radio channel has to be extended. With FAAS a fully dynamic allocation strategy of n/spl times/16 kbps subslots is proposed on a per site basis for both voice and data to optimally match the capacity requirements of high bandwidth radio channels. The approach includes bringing up and releasing Abis resources out of the Abis resource pool on demand. The interaction with admission control, radio resource management and link adaptation involving upgrade and downgrade procedures is taken into account. To avoid unacceptable voice blocking a new concept for voice protection is included. Detailed simulation results for different cell configurations are presented for voice only and mixed voice and GPRS/EDGE packet data scenarios at varying load, which allow the appropriate dimensioning of the Abis resource pool per site. Depending on the cell load capacity gains up to 70% (typically 30-40% for medium load) can be achieved compared to a static Abis allocation approach promising considerable cost savings for operators.

Contrasting GPRS and EDGE over TCP/IP on BCCH and nonBCCH carriers

The introduction of EDGE in current GSM/GPRS deployments will give operators a significant boost in network capacity and will offer mobile data users high bandwidth packet data services. Intelligent radio resource management allows the allocation of the GPRS/EDGE packet data channels (PDCHs) on the beacon carrier (BCCH) or on nonBCCH carriers. Most key performance indicators (KPIs) such as user data throughput, channel capacity and spectrum efficiency are affected by an appropriate choice of the cell configuration. In this paper detailed simulation results for the end to end performance of GPRS and EDGE over TCP/IP are presented. Todays GPRS 4 timeslot capable mobiles as well as EDGE 2 and 4 multislot mobiles are investigated. The performance of PDCH allocations on the BCCH and nonBCCH carrier has been contrasted for pure GPRS and EDGE services showing the pros and cons for each configuration. Finally mixed scenarios with GPRS and EDGE multiplexing on the same PDCHs are covered.

Breaking through AMR voice capacity limits due to dropped calls by control channel improvements in GERAN networks

During the last couple of years a series of voice quality and capacity enhancement features have been implemented in narrow-band deployments of GERAN (GSM/EDGE radio access networks) mobile radio networks. Recent field findings revealed call drop rate (CDR) to be the major limiting factor already in medium loaded AMR (adaptive multi rate) networks planned in tight frequency reuse due to excessive failures on the associated control channels (ACCH). The reason for this phenomenon observed at 20% to 30% EFL (Erlang fractional load) is the significant link level performance imbalance of up to 6 dB (in terms of C/I) between AMR 4.75/5.90 kbps voice codecs and signaling ACCH. In this study a novel strategy based on temporary ACCH overpower has been proposed as a practical and fully backwards compatible option to reduce the C/I gap and to improve the probability of successful decoding of the FACCH/SACCH frames. A full description of the CDR contributors (radio link timeout and handover failures) has been provided along with detailed system level simulation results. The initial evaluation of the novel approach is very promising, showing a significant soft capacity gain by substantially reducing CDR allowing a system load well above 30% EFL in homogeneous hexagonal networks. The suggested approach could be efficiently combined with current 3GPP standardization initiatives for control channel improvements in GERAN

Comparing frequency planning against 1/spl times/3 and 1/spl times/1 re-use in real frequency hopping networks

On the one hand, the potential of radio link control options like frequency hopping, power control and discontinuous transmission for capacity increase in GSM mobile radio networks has been extensively studied by several authors using computer simulations in homogeneous hexagonal networks. Unfortunately, some idealistic assumptions on these network models have a substantial drawback on the practical relevance of the simulation results. On the other hand, many field trials and regular network operation have proven very good results in terms of both network quality and capacity when applying radio link options in tight frequency re-use. But there, systematic investigations are hardly feasible. Therefore, we present results of close-to-reality simulations of FH networks showing that FH, PC and DTX can largely improve system capacity in real non-homogeneous networks by as much as 200%. We systematically investigate both advanced frequency assignments at varying re-use and frequency assignments in cluster 1/spl times/3 and 1/spl times/1. Our results reveal some aspects contrasting widely spread views on implementing FH in real networks. From our investigations we deduct recommendations concerning the optimum approach of using frequency hopping, power control and discontinuous transmission in GSM networks.