Wireless System Engineering and Deployment - RF Planning - Essay Example

College RF Planning RF in this context is used in place of radio frequency. It is the rate of electrical oscillations between3 kHz to 300GHZ, and it must resonate with both frequency of radio waves and the alternating currents that carry the radio signals. Now the process of assigning these frequencies, transmitter locations and all other parameters of a system of wireless communication with the aim of providing sufficient coverage and capacity for the desired service is what RF planning is. Deployment costs have to be kept as low as possible given all these activities There are two main objectives that RF planning aim to meet: The system’s ability to sustain the required number of subscribers and the geographical vastness over which the system has sufficient signal strength to provide a data session. These two aspects can be christened capacity and coverage respectively. In the quest to expand the capacity, RF planning should also strive to maintain the acceptable grade of service, and for cellular networks, good quality of speech. Additionally, the plan should allow future expansion and growth especially for the number of sites and their location (Beutler, 53). Steps involved in the planning procedure Planning is coming up with a network that can provide a service to customers at the comfort of the place they are. It can be divided into the following phases: a) Pre-planning phase This initial phase involves investigation of the properties of the future network. The operator seeks to know what kind of service the network will offer. This will then unlock the requirements the service may demand from the network. Key approximations in this phase are the area of coverage of the planned sites and the number of sites that are necessary for a given RF system. This stage does not capture the effects of the terrain which might obstruct waves (Beutler, 57). b) The main phase This second phase entails the following activities A survey is done about the area to be covered and thereafter investigation of the possible sites to set up base stations A digital map is formed which has different pixels. Data relating to the geographical properties and traffic volumes at selected points around the area are incorporated into this digital map. Calculation of the link budget. It will define the coverage threshold and the cell range. Parameters that influence the link budget are ; fade margin, base station, cable loss, antenna gain of the mobile equipment and sensitivity. Computer simulations will be done to evaluate the different possibilities to build up radio network given the link budget and the digital map. It can be done using the optimization algorithm. Optimization helps us to reach values that of greater coverage with optimal capacity at the lowest possible costs. Planning on coverage will help to determine the range of service while planning on capacity will show the number of base stations to be used (Lempiäinen, 32). Outputs which could have been produced at the end include: a list of sites and site locations, optimal frequency plan, optimal antenna directions, detailed prediction on coverage and mobility parameters for every site. c) Continuous optimization phase This last phase will involve a series of continuous adjustments with the aim of improving the network planning, which will be done through optimization of the RF constantly. This captures extra service requirement or changes in the environment. Measurement data is collected regularly through drive testing the data collected is used both in planning new sites and optimizing the parameter settings of the sites that already exist. After all this has been done, the final RF plan is ready to be deployed in the area of interest (Lempiäinen, 43). General process for RF planning Planning RF networks is generally a complex process mainly because many variables have been taken into account in the location of the base stations. I) Optimization methods of solving cost functions Given the digital map, proper mathematical models and the data needed, the best schemes of allocation can be determined by simulation. The computer searches for optimal result through the neighbors surrounding an optimal solution. The neighbor is the new value of the variable and has a 1 hamming distance from the current point (Lempiäinen, 45). In this case, neighboring solutions are an additional base station in a position that can be possible. The following four methods are applicable: Random walk-This method generates different neighbors at every iteration. Both cost functions at the new neighbor and that at the current position are evaluated and then compared. In case the old cost function is higher than the new one, the neighbor gets accepted unconditionally. The new function gets conditionally accepted if it is worse than the old function. The new function in this case is given a probability of P=O.It hence becomes the greedy search algorithm and, therefore, no solution is accepted until it gives a cost function that is more suitable, and P=1 resulting to a random search fully necessitates evaluation, at all places, of possible base station combinations. Simulated annealing-This method just follows the procedure of a random walk of calculating the cost functions of the old and generated neighbor and their subsequent comparison. It also entails unconditional and conditional accept. Different from the random walk, the probability of conditionally accepting keeps changing as we progress with the search procedure. Genetic algorithm-This idea comes from Darwinian human evolution phenomena. Sets of parent points help generate children. Children points that have the best results are selected when evaluating the cost function, compared to their parents. This method employs the use of a mutation operator which can be linked to definition of a neighborhood. Tabu search-The base station positions already selected in last k iterations (tabu) will be considered. Therefore, in finding new neighbors, they will not be considered. Normally K is taken to be 1.Resetting can be done to the size of each candidate for each iteration. As the size of the candidate is large, the final result is better. Convergence of simulations takes long. In literature, he best candidate size value can be 10 II) GSM planning This method divides a network into many cells. A base station usually is planted in the cell’s centre. Cell representation is done as neighboring hexagons for analysis’ sake. In reality, they can overlap each other and take any kind of form. When fixed, the size of cells will stay stable. GSM treats capacity planning and coverage planning as independent. Capacity planning is largely dependent on frequency allocation while coverage planning is dependent on the strength of received signal. III) UMTS planning In this method, coverage and capacity are strongly interrelated, and both play an important role in RF planning. Coverage is a function of capacity. UMTS is limited in interference. This reduces cell site, a process called cell breathing effect. RF planning tools The tools used include software packages. Some of those used in this task are: Network measurement system(NPS/X) Network planning system NPS/X works on the basis of both measurement result and utilization of digitized map. Fundamental packages include: Calculation of the coverage area Calculation of the interface area Dominance of the composite coverage area Requirements to be met by RF plan A well planned RF should have the following aspects: Coverage should be as required. It should enable easy expansion of the area covered with least system changes It should have a minimum adjustment of the antenna in the process of optimization. Maintain good service quality It should minimize changes in the database during the optimization phase. So far we have observed that RF planning is centered on planning on capacity, coverage, parameter and undertaking optimization. Network dimensioning input The input data is usually supplied by the operator. They are threefold: capacity related (traffic density map, spectrum available and subscriber growth forecast), coverage related(area types information and coverage regions) and quality related(ms classes, location probability and block probability) Basic network modules and additional elements like antenna are also important parts of the input. i) Capacity planning The first task which jumpstarts RF planning is to give the picture of the network, a process called network dimensioning. It results to estimation of equipment needed to meet capacity, quality and coverage. The network dimensioning input to that effect is quality related, capacity related and coverage related. Capacity calculation Capacity calculation is a measure of the number of subscribers a network can handle. The following steps are followed in calculation of network capacity: Based on the available spectrum and frequency re-use pattern, calculate the maximum number of carriers that can be reached per cell for different regions Find the capacity of the cell given Finally, network capacity is the sum of cumulative of cell capacities. Spectrum efficiency This is given as a multiple of channel bandwidth, re-use factor and cell area all divided by the total spectrum available. ii). Coverage planning The objective for this step is to reach a minimum number of cell sites which have optimum locations for producing coverage required for the area targeted. It is calculated with predictions modules on the digital map database. The information that should be available for coverage planning are: Coverage regions Antenna Specifications on preferred antenna system line Preferred BTS specifications Per region coverage threshold values Coverage planning involves activities such as predictions on field strength, measurement and propagation modelling. Site selection Site selection, coverage planning and site selection performed with site acquisition in an interactive manner. The two teams have their roles clearly cut out and communication means. Propagation models They are basically involved in curve fitting. Testing on propagation is done at different heights, frequencies, antenna heights and locations. These tests are done repeatedly at various distances. Mathematical tools are then used to analyze the signal data received which is latter fitted into a curve. These curves are assigned a matching formula. The generated formulas are used as models. Some examples of propagation models are: Diffraction screen model Bullington Okuruma Coverage predictions Rough coverage predictions are based on formulas derived from propagation curves. They are, however, not enough for detailed RF planning. Digital maps Information such as rods traffic density, area types and terrain heights can be digitized. In the digital form, they can be used in finding coverage predictions. Measurement of field strength These measurements are needed both when determining coverage areas and the RF planning’s propagation model. The measuring system takes samples from that signal the antenna receives. Field strength samples are recorded with marks of time and location. Average values are calculated from these samples. Point to point and cell coverage Given a digital map, path profile between two points can be obtained. Specific propagation loss can be calculated if profile is related to corresponding types of areas. The results can be useful in prediction of cell coverage. Propagation model tuning The tuning has to be done for all the types of areas in the country of interest before embarking on a detailed network planning. Cell coverage area extension It is done by preamplifiers and cellular repeaters. The RF is amplified in uplink and then in downlink directions. Connection of cellular repeater is done between two antennas. One antenna points the base station whereas the other points to an area likely to be covered. iii). Frequency planning Frequency planning is aimed at increasing efficiency of usage of the spectrum thus keeping below a certain preferred level interference in the network. It is, therefore, related to the interference predictions. There are two approaches that can solve problems in frequency assignment: The automatic frequency allocation Frequency reuse pattern The following information guides frequency allocation: Traffic density Requirement of channel on the cell basis with respect to capacity planning Limitations on channel spacing The required quality of service Performance of frequency hopping and IUO Frequency reuse At a certain distance, called reuse distance, the same frequency may be used in two cells. This distance can be shorter for digital systems. This gives digital systems an edge over analogue ones. This tendency tends to increase capacity. RF systems work on the principle of reuse of frequencies. Available frequencies are grouped into various frequency groups which together form a cluster. In a cluster, frequency groups are not reused, but only used once. The frequency groups are located at different base stations Frequency hoping It is the varying of frequency of information as dictated by a certain sequence. Frequency hopping serves to improve the service quality. iv). Parameter planning GSM radio path This is a system that uses the frame structure of time division multiple access(TDMA) consisting 8 timeslots and having a duration of 4.615 ms. Two types of channels are carried over these timeslots: Dedicated channels Common channels Common channels They are used for signaling. It has two broad categories: Broadcast channels (BCH) and common control channels (CCCH). The previous remit information on cell properties like frequency correction and neighboring cells. They are also categorized into three. The later are used in the event one wants to establish a connection between MS and BTS. Dedicated channels They have two categories: Traffic and dedicated control channels. The later perform location updating and call set up signaling procedures. Radio path measurements They are used to keep connections in the right quality. NETWORK VERIFICATION AND OPTIMIZATION This is the last step in RF planning which can be done during the period in which the network is put on trial or network expansion. The process aims at evaluating and maximizing the network’s quality of service given the quality criteria set. Network verification This step aims to evaluate the objective and independent quality of service (QOS) in a given service area. The verification procedure involves the following steps: Planning reference network, measurement resource, test route and schedule Setting quality criteria and network performance objectives Analyzing statistical result Agreeing on the likely corrective action in case of failure to meet the quality criteria set. Execution of measurement and statistical results analysis. Field verification is carried out after completion of site acceptance. It also should be done before and after major changes in the hardware or software to indicate their impact on the quality of network. Network quality criteria Customer’s quality of service and capacity requirements specifies quality objectives. Monitoring continuously the quality of service is a basic requirement when undertaking network quality survey. Then the network is compared against other networks of a similar nature and the results presented in a manner easy to understand. Sensitive metrics that are also simple to understand is required in this exercise. Analysis of the results The statistical quality sheet that is generated by networking planning system and network element availability is the result of the verification procedure. They are collected either weekly or monthly. Network optimization It is the routine process of improving network quality. Min et al, network quality can be viewed from 2 different spectra: The subscriber’s view whose view of quality is is having his service not affected and the operator’s view who concentrates on spectrum efficiency, maintenance cost, site leasing and network traffic. Network optimization services are undertaken to support the operator to improve on all aspects of quality of the network. BSS default configuration analysis module This service enables comparison of the system configuration which exists in the real network against that in the network planning. This task aims at ensuring that consistency exists in different system configuration databases. This task should be repeated routinely. BSS default parameter assessment These settings are needed to ensure the network’s best performance. Its sets of parameters are based on experience from networks that are optimized. Basic network optimization module Min et al states that field tests, customer complaints and OMC measurements are the major sources that provide a network quality picture. Actions of single quality improvement together with data analysis on network performance improve network quality. These tasks are in this module. Full optimization module This involves offering of consultancy and service in quality definition, improvement and monitoring. It is a small quality cycle used to improve the quality. This approach brings the need for a Global approach of quality improvement and monitoring. Conclusion This paper has been covering the whole process for RF planning. In detail, we have featured capacity planning, coverage planning, parameter planning and optimization planning Work cited Beutler, Roland. Frequency assignment and network planning for digital terrestrial broadcasting systems. Norwell, MA: Kluwer Academic Publishers, 2004. Print. Lempiäinen, Jukka and Matti Manninen. Radio interface system planning for GSM/GPRS/UMTS. New York: Kluwer Academic, 2002. Print. Min, Ji Hye, Min Woo Lee, Hyunchul Rhim, Dongil Choi, Young-Sun Kim, Young Jun Kim, Dong Ik Cha and Hyo K Lim. "Recurrent Hepatocellular Carcinoma After Transcatheter Arterial Chemoembolization Planning Sonography for Radio Frequency Ablation." Journal of Ultrasound in Medicine, 30. 5 (2011): 617--624. Print. Read More