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Cellular Network Optimization
Oleh: pram
January 17, 2008

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Salam…

In this post, I’ll try to share about my experience in Cellular Radio Network Optimization. This post consists of several subject that maybe useful to upgrade our knowledge and I well opened if there are questions 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, handover control : 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 management efficiently, i.e., maintaining network resources to meet customer base needs 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 developmnt process takes place. After Radio Network Planning Process and network are being implemented, Radio Tuning (a.k.a basic radio optimization) and Radio Verification have to be done to assure that the network meet the operator needs. And, after Operator have accepted the network and network UP here we go..the (extended) Optimization process is begin.

Radio Optimization is done because several causes, i.e.,



systematics inacurracies (Tool database, prediction algorithms..)
statistical processes involved (Radio Propagation, traffic..)
Assumption made
Human error (Planning errors, data entry, installation errors…)
equipment faults (hardware and software)
network growth
causes that mentioned above, could make network anomaly and it influence the customer satisfactions. So… from costumer complains statistics 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) radio Optimization to answer thoose question’s left, so we can cure the network unstability ^_^

From the description above, we can conclude that Optimization process is devided into Basic Radio Optimization and Extended Radio Optimization. Both of them are controled by O&M(Operation and Maintenance). The main difference is that the Basic Radio Optimization will be done before network launch, and Extended Radio Optimization will 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 Operator requirements. The tuning activity have to change several cell paramaters, so the quality requirement is reached. On the high coverage and traffic demands areas usually this processes will be repeated a number of times untill the system reach Optimum performance.

3. Extended Radio Optimization

This process is done as customer complains follow-up. In the real network which is loaded by customer’s traffic, it often suffer several problems that effect the customer satisfaction. From customer complains statistics we can locate the network problem and when did it took a place. After we know where and when, the Optimization team will go to that spot and do tests measurement to take a log file and check the equipment 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., laptop with tests measurement software installed, Mobile station, and GPS for outdoor case) to record logfile that contains the signaling information send 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 contains information about network configuration (network to MS direction) which is used for neighbouring cell measurements to determine cell reselections and handovers. BCCH allocation (BA) is a list of BCCH carriers in use within a specific geographical area of PLMN. It Indicates the RF Channels that the MS required to monitor while camped on a cell of that PLMN. BCCH term’s frequently used to refer to a carrier 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 or number of a channel used on the Air-interface. From the ARFCN, it is possible to calculate the frequency of the uplink and the downlink that the channel uses.

BSIC :Base station identity code. An identifier for a BTS, although the BSIC does not uniquely identify a single BTS, since it has to be reused several times per PLMN. The purpose of the BSIC is to allow the mobile station to identify and distinguish among neighbor cells, even when neighbor cells use the same BCCH frequency. Because the



BSIC is broadcast within the synchronization channel (SCH) of a BTS, the mobile station does not even have to establish a connection to a BTS to retrieve the BSIC. It consists 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 to send 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 time frame. This prevents collision with data from other mobile stations. The mechanism works fine, as long as the distance between MS and BTS is rather small. Increasing distance requires taking into account the propagation delay of downlink bursts and uplink bursts. Consequently, the mobile station needs to transmit earlier than defined by the “three time slots delay” rule. The information about how much earlier a burst has to be sent is conveyed to the mobile station by the TA. The TA is dynamic and changes in time. Its current value is sent to the mobile station within the layer 1 header of each SACCH. In the opposite direction, the BTS sends the current value for TA within the MEAS_RES messages to the BSC (e.g., for handover consideration). The farther the MS is away from the BTS, the larger is the required TA. Using the TA allows the BTS to receive the bursts from a particular MS in the proper receiver window. The BTS calculates the first TA when receiving a RACH and reports the value to the BSC. TA can take any value between 0 and 63, which relates to a distance between 0 km and 35 km. The steps are about 550 m (35 km/63 » 550 m). With respect to time, the different values of TA refer to the interval 0 ms through 232 ms, in steps of 48/13 ms. It is important to note that this value of TA represents twice 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 on power control and handover. They indicate the bit error rate that was measured on the Air-interface. The bit error rate can be determined by facilitating the training sequence. If you want to learn more… you can read the gsm recommendation

Measurements are to be taken on request from the analyzing team due to prioritizing form the coordinator. The data collection will partly consist 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 docummentation of data results must be regulated nicely, so on the post processing the analyze 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 is deal 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…

ps : hope this little post will useful… and I’m sorry if there’s a lot of mistakes. :makloem masi nyubi: