S Radio Network planning. Tentative schedule & contents

Transcription

1 S-7.70 Radio Network planning Lecturer: Prof. Riku Jäntti Assistant: M.Sc. Mika Husso Tentative schedule & contents Week Lecture Exercise. Introduction: Radio network planning process No exercise 4. Capacity planning: Traffic modeling, blocking and dropping No exercise 5. Coverage planning: Link budget, coverage probability No exercise 6 4. Frequency planning: Frequency resuse, reuse partitioning Capacity planning 7 5. Frequency planning: Channel allocation methods Coverage planning 8 6. Network planning and optimization tools Frequency planning 9 No lecture Introduction to the assignment

2 Lecture. Cellular radio systems Objectives of radio network planning Radio network planning process Cellular radio system Bandwidth is a scarce resource which needs to be divide among the users In practice all multiple access schemes introduce co-channel interference which limits the spatial reuse of the resources. Cellular radio concept (Bell Labs, 94) Service area of single base station is denoted as a cell Same frequency can be reused in spatially separates cells FDMA/TDMA NMT, GSM, TETRA, 4

3 CDMA Revolution (Qualcomm, 979) In CDMA, all cells use the same frequency. (Universal reuse) Andrew J. Viterbi, Spread Spectrum Communications: Myths and Realities, IEEE Communications Magazine May 979, Volume 7, Number IS-95, IMT000, WCDMA, 5 OFDM Systems OFDM allows flexible utilization of recourses: partial reuse, reuse partitioning, dynamic channel assignment FlashOFDM, WiMAX, LTE, 6

4 Objectives of radio network planning )To obtain sufficient coverage over the entire service area to ensure that high quality voice services and data services with low error rates can be offered to the subscribers. )To offer the subscriber traffic network capacity with sufficiently low blocking and call dropping rate. )To enable an economical network implementation when the service is established and a controlled network expansion during the life cycle of the network 7 Impact of user environment (mobility) Vehicular Efficient antennas and larger transmitter powers available in car mounted mobile stations Frequent handovers due to fast mobility Fast fading cannot be tracked by radio resource control (RRC) schemes Pedestrian Antenna shadowed by the head Battery life imposes power constraints Fast handovers in e.g. indoor outdoor movements Fast fading can be tracked by RRC 8 4

5 Impact of user environment (traffic) Low to moderate traffic Large cells Stretched cells along roads Coverage planning based on subscribers Build coverage only to dense populated areas Sparse networks: Build coverage incrementally based on Cell size subscribers Heavy traffic Small cells Multilayer networks Traffic 9 Impact of user environment (traffic) Traffic class Conversational class Streaming class Interactive class Background class Timing Real-time Non-real-time, Best effort Fundament al characterist ics - Preserve time relation (variation) between information entities of the stream - Conversational pattern (stringent and low delay ) - Preserve time relation (variation) between information entities of the stream - Request response pattern -Preserve payload content -Destination is not expecting the data within a certain time -Preserve payload content Example of the application Voice Streaming video web browsing Download, s 0 5

6 Impact of user environment (traffic) Traditionally cell planning has only been done for voice traffic Traffic classes have different requirements for grade of service (GoS) and thus need to be considered separately in the planning. Voice traffic typically requires high coverage probability and low call dropping probability while background data traffic could be designed to have smaller coverage and higher drop rates. Impact of user environment Remote areas such as wilderness and sea areas Low carrier frequency => large coverage area High base station masts Efficient antennas in the mobiles Satellite systems* *) Out of the scope of this course 6

7 Planning approaches Planning according to final network capacity all base stations are immediately built transceivers (channels) are added when traffic increases Investment cost of the network is high Unless the expected traffic is very high, the time to break even is going to be long Planning approaches Gradual improvement: In the staring phase of a network traffic is small and cell size is mainly determined by the propagation conditions, available power and receiver sensitivity (link budget). coverage is often build first on densely populated areas and along the highways. In the latter case highly directional antennas can be utilized. When the traffic increases more capacity can be obtained by using cell splitting, cell sectorization (directive antennas) and by decreasing cell size Investment costs increase gradually as the traffic increases 4 7

8 Increasing the capacity Sectored cells: Use directed instead of isotropic antennas (Requires three antennas per cell site) Sector Sector Ideally, there is no interference between the sectors. Sector Node B Radiation pattern of the antenna 5 Isotropic antennas Interference sources I ext 6 8

9 Sectored cells I ext Interference sources affecting sector 7 Sectored cells 80 deg. sectors 0 deg. sectors 90 deg. sectors 60 deg. sectors 8 9

10 Sectored cells Capacity per sector (0 degree sectors) Theoretical capacity is three times larger compared to the isotropic antenna case In practice, the antennas leak power to neighbouring sectors as well, which decreases the capacity gain. All sectors require their own pilot signals => Signalling takes more power If all the sectors have a common power amplifier, only / of the maximum power is available per cell => Capacity increase is small If all the sectors have their own power amplifier, the capacity increase is notable 9 Cell splitting ORIGINAL CELL LAYOUT SPLITTING : CELL SPLITTING :4 FINAL CELL LAYOUT 0 0

11 Hierarchical design Macrocell: Large coverage area Low bit rates (44 kbit/s) High transmit power Cell radius up to several kilometers Rural areas, suburban, city-wide coverage Microcell: Moderate coverage area Moderate bit rates (84 kb/s) Moderate transmit power Cell radius up to a few kilometers Urban area Picocells: Small coverage area High bit rates (up to Mbit/s) Small transmit power Cell radius hundreds of meters Hot spots / indoor Macrocell Picocell Microcell Hierarchical design In metropolitan areas microcells and picocells may be employed leaving the macrocells as umbrella cells. A geographical area may be covered simultaneously by all these cell types creating a multilayer network. Micro, macro, and picocells use different frequency bands even in CDMA systems to avoid frequent handovers, pilot pollution and near-far problems.

12 Novel network planning approaches New high data rate services impose new network planning challenges. High data rate services require small cells Providing any-time-anywhere broadband services (i.e. almost full coverage) would require lots of base stations and thus be very expensive 6QAM, /4 6QAM, / QPSK, /4 QPSK, / Anders Furuskär, Radio Resource Sharing and Bearer Service Allocation for Multi-Bearer Service, Multi-Access Wireless Networks, PhD Thesis, TRITA-S-RST-00, Radio Communication Systems, Dept of S, KTH, April 00. Hotspots Coverage limited, hot spot services High capacity is provided only in areas where the traffic intensity is high. Outside the hotspots, only low data rates are supported ABC: Always best connected paradigm: Service is provided using multiple radio interfaces. E.g. by using wireless local area networks (WLANs) in the hotspots and traditional cellular neteworks to support mobility and wide area coverage. 4

13 Wireless relays Range extension using wireless relays and mesh networking Wireless relay or router forwards information between user equipment and base station. There is no direct connection from the relay to the core network. Same high data rate coverage relay relay BS/AP relay R relay BS/AP relay relay 5 Wireless relays (Non-cooperative) Relaying operation consumes radio resources so the relay network has significantly less capacity than the same amount of base stations would have. Wireless relays do not require connectivity to the core network which saves in cabling costs. The complexity of the relay can vary from simple amplify and forward repeater to wireless router implementing most (if not all) the base station functionalities. Cell sites for wireless relays could be e.g. lamp posts, rooftops etc. (where ever power supply can be easily arranged). 6

14 Wireless relays Usefulness of the relaying concept depends on the cost ratio between base station and relay. H. Yanikomeroglu Network planning approaches Gradual capacity improvement using mesh networks To save in wiring cost, the initial deployment in low traffic network could be based on a mesh network where only a subset of the nodes are connected to the core network. To provide more capacity, the wireless routers can be turned to base stations by providing them access to the core network (e.g. by using high capacity optical network or high capacity microwave link) 8 4

15 Network planning Starting points for the planning procedure Desired grade (quality) of service Capacity, coverage, call dropping rate, call blocking rate, System specification Utilized bandwidth, carrier spacing, modulation and coding schemes, multiple access method, signaling methods, Equipment specification Radiation patterns of the antennas, number of supported channels, available power Available frequency band Depends on licenses provided by the regulatory authority 9 Network planning Topography and morphography of the service area Terrain height varations, nature of the ground cover (woods, open area, built-up area) building heights and density, [anything that affects radio propagation] Traffic distribution and forecast Geographic distribution of traffic and its expected growth. Some areas such as shopping malls, airports etc. are natural hotspots with high traffic intensity while some areas like woods have very little traffic. Existing infrastructure Existing antenna masts, equipment shelters, electric lines, and roads should be utilizes as efficiently as possibly 0 5

16 System specifications frequency bands carrier spacing duplex spacing access method service types and rates modulation and coding sensitivity levels for given transmission performance in different environments protection ratios for given transmission performance in different environments network tuning parameters for radio resource control (e.g. power control and handover) System specifications CDMA capacity and coverage interrelated soft capacity soft handover TDMA FDMA hard capacity hard handover capacity and coverage rather independent single rate circuit switched symmetric links RNMP_intro.dsf multi-rate packet switched asymmetric links 6

17 Grade of Service (GoS) parameters Coverage efficiency: Average base station coverage km /number of base stations Area location probability/coverage probability Probability that a randomly positioned UE can be served with certain QoS level (usually stated in term of Signal-tointerferece+noise ratio SINR) Received power (noise rise, load factor) [important in CDMA systems] Capacity kbs/hz/cell Throughput kbs Outage probability Probability that a user can not achieve its QoS target (usually stated in terms of SINR) Blocking probability Probability that a new user is denied access to the network Dropping probability Probability that a on-going call is terminated due to overloading. Phases of the planning procedure. Capacity planning based on the actual network specification, traffic information, available bandwidth, and GoS (blocking and dropping). The output of this phase is the preliminary capacity plan giving cell sizes and number of channels in each cell.. Coverage planning based on the results of the preliminary capacity plan, equipment specifications, system specification, especially the required receiver sensitivity. The output of the coverage plan are e.g. equipment parameters needed to obtain a specified coverage percentage or the coverage prediction with given equipment parameters. 4 7

18 Phases of the planning procedure Frequency planning based on the results from the capacity and coverage planning. In addition, protection ratios for co-channel and adjacent channel interference, usually given in the system specification, are needed. With same methods as in the coverage planning the frequency reuse distance is determined. This information, together with rules for the use of adjacent carriers, is used to make channel allocation to the base stations. In CDMA-networks very little frequency planning is needed (only for hierarchical cell layouts). Instead a code reuse planning is neded. 5 Network planning process Operators GoS requirements Area type Propagation conditions Dimensioning Coverage plan (Link budget) Capacity plan (Erlang capacity) Frequency plan Network planning Simulation Visulisation Optimisation Tuning of RRM parameters Network optimization Rough number of base stations Rough estimate of Base station sites and their configuration Site selection Base station configurations Parameters for RRM algorithms Capacity and coverage estimate QoS Measurements of network performance 6 8

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