Influence problem and solution of EGPRS network quality
Author: He YanMin Meng FanLi Wei KeMin Bai Yu 1,EDGE( EGPRS) About critical technology The data rate that EGPRS form time slot offers is 3 times that of GPRS in theory, the maximum speed of the single time slot is from 21.4kbit/s( CS4) of GPRS Improve to 59.2kbit/s( MCS9) ,If truss up and use 8 time slots, the data rate reachable 473kbit/s of maximum. This kind of speed can support the multiple operation such as Internet's having a look around, video teleconference and high-speed E-mail, offer the multimedia communication to user before 3G network. The ability that EGPRS bears the weight of the data traffic is stronger than GPRS technical reason to mainly lie in EGPRS has adopted the following critical technology. 1.1 8PSK modulation method - -Have raised the transmission rate EGPRS adopt the intersection of advanced person and the intersection of time slot and operate and the intersection of 8PSK and modulation technique much, under compare with, GMSK modulation that GPRS adopt have good antijamming capability, but the transmission rate is lower; 8PSK modulating speed is 3 times that of GMSK modulation, but the stupid key (Robustness) of the signal Relatively GMSK is bad, reflect to frequency deviation, noise, time delay,etc. sensitively, it is weaker than GMSK to resist frequency deviation, noise, time delay ability. 1.2 Mixed coding scheme - -Have improved the handling capacity of the data The coded method of the MCS modulation incorporates the fault-tolerant protection mechanism in the coding scheme, among them MCS1- MCS4 adopts GMSK modulation method, fault-tolerant protective power is strong, the throughput of the data is relatively lower; MCS5- MCS9 adopts 8PSK modulation method, the data are stronger in handling capacity. 1.3 Quality control algorithm of the enhanced periodic line - -Have raised data transmission and receiving efficiency EGPRS has adopted the enhanced periodic line control algorithm of adaptation of the periodic line and incremental redundancy, achieve the signal channel data throughput rate of maximum, raise and receive the proper really probability of receiving and correct demodulation. In addition, EGPRS has adopted advanced technology too in interweaving, addressing window,etc., in order to offer the higher, more stable transfer rate. 2,The project influences case study and solution of network quality while employing After the staging EGPRS of the network, the impact on network capability can carry on the discussion from several following respects. 2.1 Influence the factor analysis of the quality of transmission of EGPRS wireless network EGPRS speed of crest value of the maximum achievable 473kbit/s of every frame when 8 time slots are bound, but this speed will receive environment of transmission over radio, binding and restriction of the modulation mode of many time slots. 2.1.1 Many time slots are trussed up and signal channel multiplexes EGPRS supports the signal channel to multiplex, can raise network capacity and efficiency effectively. When EGPRS does not share the signal channel with GPRS, each EGPRS time slot supports 9 to descent in user and 7 upstream users at most. The mobile phone can carry on the time slot and multiplex in GPRS system, can be used in the ascending-descending and work respectively with 8 time slots at most, commercial the intersection of mobile phone and a most frequently used one the intersection of 1U and +3D, another kinds of the intersection of 2U and the intersection of test and Mobile of +4D at present. To EGPRS cell-phone of 1U +3D, the speed is 59.2* 3 that the maximum that can reach descents =177.6kbit/s, the upstream speed is 59.2kbit/s. In this case, the quality of the wireless network environment seems very important to the influence of the transmission rate. 2.1.2 Wireless environment (C/I) Influence EGPRS has relatively high expectations for wireless environment, EGPRS MCS6- MCS9 encoder mode requires C/I about 12- 20dB. In order to realize 40- 50kbit/s transmission rate, C/I requires about 20- 25dB. Fig. 1 represents under different encoder modes, the relation of speed of download of time slot of EGPRS form and C/I. Relation of speed of download of time slot of Fig. 1 EGPRS form and C/I Can be found out from Fig. 1, when C/I is smaller than 18dB, MCS6- MCS9 characteristic is very bad, the transfer rate is even lower than MCS1- MCS5; When C/I is greater than 20dB, change gradually in characteristic well, the transfer rate can even be in order to exceed 50kbit/s. In order to obtain good transmission rate, can choose to open EGPRS on the signal channel that C/I quality is better, such as BCCH signal channel. 2.1.3 Influence to EGPRS of GPRS upstream data transmission When EGPRS terminal station is being downloaded, a GPRS terminal established connection uploads the data on correspondent TSL at the same time, in order to make GPRS terminal station solve USF out, EGPRS is terminal to download the machine format code to drop to GMSK way from 8PSK, the direct influence EGPRS characteristic. Through downloading to EGPRS alone separately, GPRS and EGPRS download together and GPRS upload / download three situation by EGPRS result tested to go on relatively produce the following result respectively: ( 1) Throughput is the highest when EGPRS downloads alone; ( 2) GPRS and EGPRS are 70% of the speed when EGPRS downloads alone while downloading together; ( 3) GPRS upload / download speed, can drop suddenly download, by EGPR, only slightly high than GPRS; ( 4) At the time of GPRS and EGPRS shared channel, GPRS has significant influence on EGPRS business. In order to avoid the impact on EGPRS of GPRS business, can follow the proportion of recoverable amount of the GPRS cell-phone and EGPRS cell-phone in the network, choose GPRS in areas such as GPRS terminal more county towns,etc. and EGPRS shared channel, choose GPRS and the intersection of EGPRS and the intersection of opening and tactics of shared channel in the intersection of EGPRS and the intersection of terminal more urban area and intensive urban area,etc. and area. 2.1.4 Influence of cell reselecting In a situation that EGPRS and GPRS mix the network, the cell reselecting especially between EGPRS and GPRS, will influence the throughput of the data, influence degree depends on the time scale of service of EGPRS and GPRS Residential Area. While testing actually, can see obvious transmission rate drops while carrying on cell reselecting. In EGPRS discontinuous overlay area, EGPRS will make the real-time speed of the system drop to GPRS cell reselecting, thus influence the average performance of the system. It is cut off that the ones that will cause data traffic in cell reselecting are transient, but GPRS EGPRS cell reselecting and EGPRS EGPRS and GRPS There is no obvious difference in the long respect while cutting off of cell reselecting between GPRS. At the same time, because the overlay area of EGPRS Residential Area is smaller than the overlay area of Residential Area of GSM/GPRS, need to set up the appropriate cell reselecting parameter in the excellent work of the network to control the reselection range of EGPRS Residential Area, avoid carrying on cell reselecting in user's intensive area of data. 2.1.5 EGPRS wireless network planning EGPRS wireless network design focus concentrates on the following respects: PDCH/EPDCH the intersection of signal channel and planning, the intersection of PCU and the intersection of capacity and planning, the intersection of Gb and the intersection of interface and planning, base station Abis transmit the demand to plan. Especially the openning of EGPRS, have greater transmission dilatation demands to interface of Gb interface and Abis, in a situation that the network can not reach the requirement of goal while transforming now, it is apt to form and transmit the bottleneck. The network capability disposes the insufficient handling capacity that will reduce EGPRS wireless network seriously, have influence greatly in giving play to the characteristic of EGPRS network.