Salam… Cellular Network Optimization
In this post, I’ll try to share about my experience in CellularRadio Network Optimization. This post consists of several subject thatmaybe useful to upgrade our knowledge and I well opened if there arequestions relate to those subject. Please feel free to discuss with me,you can post it on comment or send email.
Why Optimization?
Below, I’ll mention optimization objectives generally,
increasing network availability (deal with call performances, i.e.,drop calls reduction to increase the access completion rates, handovercontrol : assure enough handover to cover costumers mobility)
increasing network quality (deal with speech and data quality to increase customer satisfaction)
increasing network capacity (deal with capacity managementefficiently, i.e., maintaining network resources to meet customer baseneeds so the blocking possibility is minimum)
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well… after we’ve talked about optimization aims, below we’ll discuss about optimization
procedures. First, we need to know how’s the network developmntprocess takes place. After Radio Network Planning Process and networkare being implemented, Radio Tuning (a.k.a basic radio optimization)and Radio Verification have to be done to assure that the network meetthe operator needs. And, after Operator have accepted the network andnetwork UP here we go..the (extended) Optimization process is begin.
Radio Optimization is done because several causes, i.e.,
Human error (Planning errors, data entry, installation errors…)
equipment faults (hardware and software)
network growth
causes that mentioned above, could make network anomaly and itinfluence the customer satisfactions. So… from costumer complainsstatistics we know where and when does the
network unstability take a place. Hmm…is there any left behind?? yup…we have to know what, why, and how…We need The (extended) radioOptimization to answer thoose question’s left, so we can cure thenetwork unstability ^_^
From the description above, we can conclude that Optimizationprocess is devided into Basic Radio Optimization and Extended RadioOptimization. Both of them are controled by O&M(Operation andMaintenance). The main difference is that the Basic Radio Optimizationwill be done before network launch, and Extended Radio Optimizationwill be done after network is launched with normal subscriber. 2. Basic Radio Optimization (Radio Tuning)
System Tuning is done on this process, in order to meet the Operatorrequirements. The tuning activity have to change several cellparamaters, so the quality requirement is reached. On the high coverageand traffic demands areas usually this processes will be repeated anumber of times untill the system reach Optimum performance. 3. Extended Radio Optimization
This process is done as customer complains follow-up. In the realnetwork which is loaded by customer’s traffic, it often suffer severalproblems that effect the customer satisfaction. From customer complainsstatistics we can locate the network problem and when did it took aplace. After we know where and when, the Optimization team will go tothat spot and do tests measurement to take a log file and check theequipment conditions.
The tests measurement and equipment conditions data will be analyzed to make recommendation so the network problem can be fixed. 4. Tests Measurements
This activity is carried out with test mobile system (i.e., laptopwith tests measurement software installed, Mobile station, and GPS foroutdoor case) to record logfile that contains the signaling informationsend over the air interface and will consists following paramaters:
Information for channel in use (serving cell):
BCCH
ARFCN
BSIC
TIMING ADVANCE
TX POWER (MS)
RX Qual
RX Lev
Information for handover candidates (neighbors cell)
BCCH
BSIC
RxLev
note : on my projects, I use TEMS investigation 4 or above..
Hmm.. before we go to the next subject, we have to know the deffinition of paramaters which is mentioned above. ^_^
BCCH : Broadcast Control Channel is a key channel containsinformation about network configuration (network to MS direction) whichis used for neighbouring cell measurements to determine cellreselections and handovers. BCCH allocation (BA) is a list of BCCHcarriers in use within a specific geographical area of PLMN. ItIndicates the RF Channels that the MS required to monitor while campedon a cell of that PLMN. BCCH term’s frequently used to refer to acarrier or a channel that often lead to confusion. Well on this case,it means carrier or channel.
ARFCN : Absolute radio frequency channel number. An identifier ornumber of a channel used on the Air-interface. From the ARFCN, it ispossible to calculate the frequency of the uplink and the downlink thatthe channel uses.
BSIC :Base station identity code. An identifier for a BTS, althoughthe BSIC does not uniquely identify a single BTS, since it has to bereused several times per PLMN. The purpose of the BSIC is to allow themobile station to identify and distinguish among neighbor cells, evenwhen neighbor cells use the same BCCH frequency. Because the
BSIC is broadcast within thesynchronization channel (SCH) of a BTS, the mobile station does noteven have to establish a connection to a BTS to retrieve the BSIC. Itconsists of the network color code (NCC), which identifies the PLMN,and the base station color code (BCC).
TA : Timing advance. The agreement in a GSM system is for the MS tosend its data three time slots after it received the data from the BTS.The BTS then expects the bursts from the MS in a well-defined timeframe. This prevents collision with data from other mobile stations.The mechanism works fine, as long as the distance between MS and BTS israther small. Increasing distance requires taking into account thepropagation delay of downlink bursts and uplink bursts. Consequently,the mobile station needs to transmit earlier than defined by the “threetime slots delay” rule. The information about how much earlier a bursthas to be sent is conveyed to the mobile station by the TA. The TA isdynamic and changes in time. Its current value is sent to the mobilestation within the layer 1 header of each SACCH. In the oppositedirection, the BTS sends the current value for TA within the MEAS_RESmessages to the BSC (e.g., for handover consideration). The farther theMS is away from the BTS, the larger is the required TA. Using the TAallows the BTS to receive the bursts from a particular MS in the properreceiver window. The BTS calculates the first TA when receiving a RACHand reports the value to the BSC. TA can take any value between 0 and63, which relates to a distance between 0 km and 35 km. The steps areabout 550 m (35 km/63 » 550 m). With respect to time, the differentvalues of TA refer to the interval 0 ms through 232 ms, in steps of48/13 ms. It is important to note that this value of TA representstwice the propagation delay.
Tx Power (MS): Power transmited by Mobile Station
RxLev: RXLev provides the results of the measurement of the receiving level on the
Air-interface. These measurements are performed independently by the MS and the BTS. On this case RxLev is measured on the MS.
RxQual : RXQUAL values, are relevant for the decision of a BSC onpower control and handover. They indicate the bit error rate that wasmeasured on the Air-interface. The bit error rate can be determined byfacilitating the training sequence. If you want to learn more… you canread the gsm recommendation
Measurements are to be taken on request from the analyzing team dueto prioritizing form the coordinator. The data collection will partlyconsist of pure measurements and a pre analysis of the collected data.
Data collection can be divided in to three parts:
- continuous drive test (drive over an area to detect poor coverage, handover missed, interference..etc)
- spot drive test (dedicated measurement on specific problem spots for detail analyzing of particular problem)
- network performance test (typical measurements over a hugh area i.e.,town or road distance, such as: Call Success Test, Quality level, etc.)
Should be noted that after each data collecting, the docummentationof data results must be regulated nicely, so on the post processing theanalyze team can use that results easily.
well…if there’s no question, I’ll go to the next subject.
5. Measurement Analysis
The main goal of Optimization process is to improve the network performance. This is the list of analysis :
- signal strength (is checked according specified mobile classes inside actual coverage area)
- adjacent and cochannel interference
- handover pattern (to avoid “Ping Pong” handover)
The results of these analysis is Technical Recommendation wich isdeal with action request for equipment config change both hardware(antenna configuration,etc.) and software (RF parameters).
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I think is enough for this post, I’m afraid it’s too theoretically :P.Hmm.. maybe on the next chapter.. I’ll post a little bit “practical”,about tools, about TEMS, about hardware, about post processing, etc.Just wait and see…
wassalam…
Thanks: 
Cellular Network Optimization
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