cdma正常信令及异常信令分析呼叫处理流程及网络优化.ppt

呼叫处理流程及网络优化,内容,第一部分 呼叫流程 第二部分 常规掉话、接入失败及掉话分析。,cdma呼叫过程,第一部分,cdma 呼叫处理,acquisition of the cdma system idle mode handoff registration termination origination end of a call handoff,手机是怎么工作的?,acquisition of the cdma system,cdma 呼叫过程,手机找到一个频率,手机发现最强的导频信号, 读取同步信道信息,配置信息,读完同步信息后，手机开始读寻呼信道消息，并开始不停监测该信道。 在通话前，手机必须收集到完整的配置信息。 配置信息每 1.28 seconds会重复。 有新的消息手机会更新，如没有600s手机也会更新一次,手机到寻呼信道获得配置信息,2个重要的配置信息,4个另外的配置信息,idle 模式下的切换,cdma 呼叫流程,idle 模式下的切换,idle模式下总是解调最强信号。 手机不停搜索临区的导频。 如果手机发现更好的信号，就切换上去，基站并不知道。,idle 模式下的手机行为,手机在接入信道的操作,1个寻呼信道对应32个接入信道. 接入信道在开环模式下工作! 手机探针工作如下： if “probe” not acknowledged by bts within acc_tmo (400 ms.), phone will wait a random time (200 ms) then probe again, stronger by pi db. there can be 15 max. (typ. 5) probes in a sequence and 15 max. (typ. 2) sequences in an access attempt most attempts succeed on first probe!,登记,cdma 呼叫处理过程,登记,登记就是空闲模式下的手机让系统知道它在等待呼入电话。 this allows the system to inform the mobiles home switch of the mobiles current location, so that incoming calls can be delivered registration also allows the system to intelligently page the mobile only in the area where the mobile is currently located, thereby eliminating useless congestion on the paging channels in other areas of the system there are many different conditions that could trigger an obligation for the mobile to register there are flags in the system parameters message which tell the mobile when it must register on the current system,一个登记实例,the system parameters message tells all mobiles when they should register. this mobile notices that it is obligated to register, so it transmits a registration message.,the base station confirms that the mobiles registration message was received. were officially registered!,起呼,cdma 呼叫处理流程,手机起呼,手机用户按 send键. 手机发射 origination message 在接入信道上. 系统在寻呼信道上确认接受到该消息. 系统为呼叫准备资源. 基站在寻呼信道上发channel assignment message. 手机和基站在业务信道关注相互确认消息。. 呼叫建立完成.,手机起呼,the mobile sends an origination message on the access channel.,the base station confirms that the origination message was received.,the base station sends a channel assignment message and the mobile goes to the traffic channel.,业务信道确认,连接完成,now the switch completes the audio circuit and the two callers can talk!,被叫,cdma 呼叫处理过程,一个实际的来电呼叫,the system pages the mobile, 615-330-0644.,the base station confirms that the mobiles page response was received. now the mobile is waiting for channel assignment, expecting a response within 12 seconds.,the mobile responds to the page.,信道分配和业务信道确认,only about 400 ms. after the base station acknowledgment order, the mobile receives the channel assignment message.,the base station is already sending blank frames on the forward channel,using the assigned walsh code.,the mobile sees at least two good blank frames in a row on the forward channel, and concludes this is the right traffic channel. it sends a preamble of two blank frames of its own on the reverse traffic channel.,the base station acknowledges receiving the mobiles preamble.,the mobile station acknowledges the base stations acknowledgment. everybody is ready!,呼叫建立完成,now that both sides have arrived on the traffic channel, the base station proposes that the requested call actually begin.,the mobile agrees and says its ready to play.,the base station orders the mobile to ring, and gives it the calling partys number to display.,18:14:48.018 reverse traffic channel: order ack_seq: 1 msg_seq: 4 ack_req: 0 encryption: 0 mobile station acknowledgement order,the mobile says its ringing.,service connect complete is a major milestone in call processing. up until now, this was an access attempt. now it is officially a call.,正式通话,the mobile has been ringing for several seconds. the human user finally comes over and presses the send button to answer the call.,now the switch completes the audio circuit and the two callers can talk!,结束一个通话,cdma 呼叫处理过程,正常通话结束,at the end of a normal call, this mobile user pressed end.,the mobile left the traffic channel, scanned to find the best pilot, and read the sync channel message.,the base station acknowledged receiving the message, then sent a release message of its own.,切换,cdma 呼叫处理过程,呼叫已经建立了，手机还在搜索信号,ec/io,all pn offsets,0 0,32728 512,chips pn,0,-20,neighbor set,the call is already in progress. pn 168 is the only active signal, and also is our timing reference. continue checking the neighbors.,if we ever notice a neighbor with ec/io above t_add, ask to use it! send a pilot strength measurement message!,t_add,10752 168,32000 500,14080 220,!,!,手机切换!,just prior to this message, this particular mobile already was in handoff with pn 168 and 220. this pilot strength measurement message reports pn 500 has increased above t_add, and the mobile wants to use it too.,the base station acknowledges receiving the pilot strength measurement message.,基站发切换消息,the base station sends a handof direction message authorizing the mobile to begin soft handoff with all three requested pns. the pre-existing link on pn 168 will continue to use walsh code 61, the new link on pn220 will use walsh code 20, and the new link on pn500 will use walsh code 50.,the mobile acknowledges it has received the handoff direction message.,手机执行切换,the mobile searcher quickly re-checks all three pns. it still hears their pilots! the mobile sends a handoff completion message, confirming it still wants to go ahead with the handoff.,18:14:54.920 forward traffic channel: order ack_seq: 0 msg_seq: 1 ack_req: 0 encryption: 0 use_time: 0 action_time: 0 base station acknowledgement order,base station acknowledgment,98/05/24 23:14:02.985 rtc handoff completion message msg_length = 72 bits msg_type = handoff completion message ack_seq = 6 msg_seq = 1 ack_req = 1 encryption = encryption mode disabled last_hdm_seq = 0 pilot_pn = 168 offset index pilot_pn = 220 offset index pilot_pn = 500 offset index reserved = 0,handoff completion message,the base station confirms it has received the mobiles handoff completion message, and will continue with all of the links active.,邻区更新，切换完成,in response to the mobiles handoff completion message, the base station assembles a new composite neighbor list including all the neighbors of each of the three active pilots. this is necessary since the mobile could be traveling toward any one of these pilots and may need to request soft handoff with any of them soon.,the mobile confirms receiving the neighbor list update message. it is already checking the neighbor list and will do so continuously from now on. the handoff is fully established.,切换完成，手机还在搜索信号,软切换规则,激活集、候选集、邻小区集、剩余集。 手机发 pilot strength measurement message 消息的条件: it notices a pilot in neighbor or remaining set exceeds t_add an active set pilot drops below t_drop for t_tdrop time a candidate pilot exceeds an active by t_comp,一个完整的切换后的导频图,导频搜索的顺序,总结：被叫流程,总结：切换流程,cdma 优化,第二部分,cdma rf 指示,fer 误帧率 on forward channel (realized at handset) on reverse channel (realized at base station) fer is an excellent call quality “summary” statistic rxpwr 手机接收信号强度 usually expressed in dbm measured derived from handset if agc broadband, “unintelligent” measurement: includes all rf in the carrier bandwidth regardless of source, not just rf from serving bts,rx level,forward,reverse,cdma rf 指示,ec/io “cleanness” of the pilot foretells the readability of the associated traffic channels guides soft handoff decisions digitally derived: ratio of good to bad energy seen by the search correlator at the desired pn offset never appears higher than pilots percentage of serving cells transmitted energy can be degraded by strong rf from other cells, sectors imperfect orthogonality, other pns are -20 db. can be degraded by noise,ec,io,energy of desired pilot alone,total received power spectral density, including signal and interference,cdma rf 指示,pilot strength (ec/io),+43dbm (20watts),-3db,+12db,eirp= +52dbm,pilot = 3 watts paging = 2 watts sync = 1 watt traffic = 14 watts,pilot,paging,sync,traffic 1,traffic 2,traffic k,power,cdma bs bandwidth,fixed over- head power,20 w,6 w,3 w,exercise: calculate the transmitted ec/io from this bts,cable loss,cdma rf 指示,pilot strength (ec/io),+43dbm (20watts),-3db,+12dbi,eirp= +52dbm,pilot = 3 watts paging = 2 watts sync = 1 watt traffic = 14 watts,pilot,paging,sync,traffic 1,traffic 2,traffic k,power,cdma bs bandwidth,20 w,3 w,cable loss,ec,io,ec/io = 10 log(3/20) = - 8 db,cdma rf 指示,txpwr 手机发射功率 actual rf power output of the handset transmitter, including combined effects of open loop power control from receiver agc and closed loop power control by bts cant exceed handsets maximum (typ. +23 dbm) txga transmit gain adjust sum of all closed-loop power control commands from the bts since the beginning of this call,typical txpwr: +23 dbm in a coverage hole 0 dbm near middle of cell -50 dbm up close to bts,txpwr = -(rxdbm) -c + txga c = +73 for 800 mhz. systems = +76 for 1900 mhz. systems,cdma 信号特征,cdma 优化,“比较好的环境,the key cdma rf performance indicators provide powerful clues in cause-and-effect analysis for understanding problem conditions there are many common conditions which are easy to recognize from their characteristic “signatures” - unique relationships among the key indicators which are observed when these conditions exist we will use the simplified format shown at right to display the key indicators for each of several interesting cases.,好的呼叫的环境,if the mobile station originates successfully, remains in service area, and makes normal release, data will show: low forward fer receive power -100 dbm good ec/io ( -12 db) normal transmit gain adjust (actual value depends on site configurations, loading & nom_pwr setting) transmit power +20 dbm good messaging parsed message files will contain a full set of normal messages.,弱覆盖环境,if a mobile station is taken out of the service area or into a coverage hole, and only data from the mobile station is available, the log files will show the following characteristics: high forward fer low receive power ( +20 dbm) poor messaging on both links,前向干扰环境,characteristics of data for a phone experiencing forward link interference from a source other than the current bts: high forward fer good receive power ( -100 dbm) low ec/io ( -10 db) higher-than-normal transmit gain adjust normal transmit power ( +20 dbm) poor forward link messaging unreliable and may be the actual cause of the drop.,反向干扰,characteristics of data for a phone whose bts has a raised noise floor due to reverse link interference good forward fer good receive power ( -100 dbm) good ec/io ( -10 db) higher-than-normal transmit gain adjust higher-than-normal transmit power ( +20 dbm) poor reverse link messaging in the message files, youll see repeats of messages on the forward link and reverse link,信息接受规则,系统重复5次，都没回馈，将丢弃本次通话。 手机重复3次，都没回馈，将丢弃本次通话。,掉话例子,this dropped call is a dramatic example of big forward link problems. as the call begins, forward fer is low with good ec/io, rxpwr, txpwr, and txga. rxpwr gets steadily better, txpwr and txga are climbing.,at 18 seconds, suddenly ec/io withers, fer explodes, and both tx and txga increase. after four seconds, we recover but briefly ec/io dives again and fer roars while rxpwr, txpwr and txga rise . at 30 seconds, fer is so bad that the transmitter mutes. ec/io recovers briefly but falters again and we mute at 34 seconds. rxpwr, txpwr, and txga are all high. ec/io briefly recovers, but then fades. the call slides to an ugly death.,常见的cdma问题,cdma 优化,接入失败问题,接入失败可能在下列节点出现: access probes exhausted (not received by system) access probes exhausted (seen by system but ack not reaching mobile station) ack received by mobile station but channel assignment message not seen channel assignment message seen at mobile but mobile station does not acquire forward traffic channel mobile station acquires forward traffic channel but system does not acquire reverse traffic channel system acquires reverse traffic channel but service connect message is not seen at mobile station.,if the failures occur in areas where one bts is dominant, suspect bts hardware problems. plot the access failures to see if they correlate with areas of bts overlap. if so, suspect forward link problems. this is probable because the mobile does not have the normal advantage it would get from soft handoff on a traffic channel. during access, it must successfully demodulate all five bts messages without the benefit of soft handoff. if the handset is in an area of multiple bts overlaps or weak signal, this can be risky. in such cases, try to make the serving bts more dominant. also check the access/probing parameters.,if the base station never sees the mobiles probes, the cause is probably coverage-related. if it happens in strong signal areas, suspect bts hardware. check datafill for proper nom_pwr and pwr_inc. be sure the bts datafill access channel acquisition and demodulation search windows are adequate.,如何减少接入失败,掉话原因,if the radio link fails after the mobile sends the service connect complete message then it is considered a dropped call. using the signatures described earlier, it is possible to recognize and separate the dropped calls into the categories at right. each category has its own causes and solutions dropped call analysis can consume a considerable amount of time. using good post-processing analysis tools, the root cause of some of the drops can be determined from mobile data alone. however, there will be cases where the cause cannot be reliably confirmed unless system data is also used,“对切换慢导致掉话处理,when the mobile is suddenly confronted with a strong new signal, or when the signal it is using takes a sudden deep fade, poor ec/io and high forward fer will occur. the call will drop unless it gets help quickly. several steps which must occur without delay: the mobile search correlator must first notice the new pilot and send a psmm to the system. the system must set up the soft handoff and notify the mobile. the mobile must acquire the new signal by locking a finger,sources of delay causing slow handoff,延迟可能发生在下列过程中： mobile search correlator notices new pilot window sizes too large, searching is slow multi-sector soft handoff already underway, many active pilots, searching is slow interferer is not a neighbor, must find in remaining set: mobile is very slow searching remaining set system cannot recognize or use remaining-set pilots! mobile reports psmm to system. reverse link noisy, psmm must be re-requested & repeated system sets up handoff, sends ehdm to mobile resource congestion: no tces, or no forward power available forward link is noisy, mobile doesnt hear ehdm, must repeat fortunately, these problems are avoidable!,搜索窗定义,the phone chooses one strong sector and “locks” to it, accepting its offset at “face value” and interpreting all other offsets by comparison to it in messages, system gives to handset a neighbor list of nearby sectors pns propagation delay “skews” the apparent pn offsets of all other sectors, making them seem earlier or later than expected to overcome skew, when the phone searches for a particular pilot, it scans an extra wide “delta” of chips centered on the expected offset (called a “search window”) search window values can be set individually for each pilot set (active & candidate, neighbor, and remaining) th