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RAVI SHARMA (KCS-711) Mobile Computing Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 1 RAVI SHARMA (KCS-711) Mobile Computing Mobile Computing R...
RAVI SHARMA (KCS-711) Mobile Computing Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 1 RAVI SHARMA (KCS-711) Mobile Computing Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Mobile Objects Communication Network Computation RAVI SHARMA (KCS-711) Mobile Computing Designing a Communication System RAVI SHARMA (KCS-711) Mobile Computing that can handle Computation R A V I S H A R M A in ( KaC Network S-711) of Mobile Objects Mobile Computing 2 Application Span of Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Communication Data – WWW – Banking / Payment Wallets Audio, Video, Photo, Email Card Authentication, Portal – Cellular Login, Payments R A V I S H Audio, A R MVideo, A ( KSMS, C S -MMS 711) – Database M o Management bile Computing – Satellite ERP, Inventory – Vehicular R A Sensing VI SHARMA (KCS-711) Actuation/Control Mobile Computing – Weather forecast – UAV / UGV – Land, River-bed monitoring – Guided missiles – Coordinate Air Strikes RAVI SHARMA (KCS-711) Mobile Computing 3 Example: Smart Phone RAVI SHARMA (KCS-711) Mobile Computing R ASmart V I S Hphones A R M A are ( K designed C S - 7 1 1 ) for hands-in and M on-the-fly o b i l e C o usages m p u t i and ng hence stand as a primary example for mobile computing. It can perform Audio, Video, Text and Image based interactions by R Amultiple V I S H Awireless R M A ( standards: K C S - 7 1 1 )Cellular, WiFi, Bluetooth M o b i l e etc. Computing As an example, It carries significant computing capability to support: – Real-time navigation and tracking R A –V IImage SHA R M A (techniques processing K C S - 7 1for 1 live ) interactions Mobile Computing – Process management for performance optimization It also supports cross-protocol communication (heterogeneous RAVI SHARMA (KCS-711) Mobile Computing Networking) – WiFi calling – HotSpot 4 What is Mobile Computing? RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Mobile computing can be described as a computing environment having objects capable of physical mobility. It envisions seamless provisioning of computation and R A communication V I S H A R M A ( Kcapability C S - 7 1 1 through ) M of a network o bmobile i l e C oobjects. mputing In addition to providing the above two capabilities anywhere and R A anytime, V I S H A RItMalso A ( involves K C S - 7 1dealing 1) with the limitations M o b i l e of C ounderlying mputing hardware, software and networking. – For example: Resource management: Energy, Network, Database R A V I S H Security ARMA (KCS-711) Mobile Computing Interoperability among protocol standards 5 Four Paradigms / Principles RAVI SHARMA (KCS-711) Mobile Computing R A Portability VI SHARMA (KCS-711) Mobile Computing – Devices/nodes in a mobile computing environment, should have sufficient processing capability and physical portability to operate. Connectivity R A V–I Given S H A Rthe M Acapability ( K C S -of7 1devices/nodes 1) to move,M networking o b i l e C oinm ap u mobile ting computing system should provision maximum availability with minimum performance degradation. Interactivity RAVI SHARMA (KCS-711) Mobile Computing – The devices/nodes within a mobile computing system should be capable of communicating and collaborating towards data transactions Individuality R A V–I AS Hmobile A R M computing A ( K C S - system 7 1 1 ) should be capableM of o bproviding ile Com p u t i to services ng individual devices/nodes and acquiring its contextual information while adopting the technological heterogeneities in-between. 6 RAVI SHARMA (KCS-711) Mobile Computing Issues / Challenges in RAVI SHARMA (KCS-711) Mobile Computing Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 7 RAVI SHARMA (KCS-711) Mobile Computing Battery Consumption Quality of Storage Limitations Communication RAVI SHARMA (KCS-711) Mobile Computing Privacy RAVI SHARMA (KCS-711) Mobile Computing 8 Issues/Challenges RAVI SHARMA (KCS-711) Mobile Computing Resource RAVI SHARMA (KCS-711) Mobile Computing – A finite amount of battery power accompanies the requirements of computation and communication on the fly – Technologically, hardware and software advancements for both computation and power optimization are ongoing R A V– I Data: S H AStorage R M A management ( K C S - 7 1 1(Distribution, ) Replication, M o bSecurity) ile Computing Communication – Mobile communication is prone to: Interference from other radios R A V I S HPerformance A R M A ( variability K C S - 7 due 1 1 )to bandwidth limitations M ocausing b i l e latency Computing Topological and Signal Propagation anomalies Security – Privacy preserving protocols are required for target application. RAVI SHARMA (KCS-711) Mobile Computing – Mobile devices are more susceptible to physical damage or loss than static systems. 9 Issues/Challenges RAVI SHARMA (KCS-711) Mobile Computing Interoperability RAVI SHARMA (KCS-711) Mobile Computing – Heterogeneity in hardware and software standards among devices and regions of operations Accessibility – Limiting size of mobile devices interfaces e.g. touchscreen, keypads makes it R A V I difficult S H A R for M A the ( K user C S - 7to1 1interact. ) It results inMao trade-off b i l e C obetween m p u t i nthe g capability to be mobile and performance. Hazards – Cellular radiation v/s health RAVI SHARMA (KCS-711) Mobile Computing – Cell phones v/s medical instruments – Distraction while Driving Accidents† – 2019: 23K RAVI SH A– R2020: M A16K( KCS-711) Mobile Computing † Road Accidents in India, Ministry of Road Transport and Highways, Government of India, Source: https://morth.nic.in/road-accident-in-india 10 RAVI SHARMA (KCS-711) Mobile Computing Wireless RAVI SHARMA (KCS-711) Telephony Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 11 Generations RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Generation advancement in Wireless Telephony refers to the evolution of fundamental nature of the service R ARestricted/non-backward V I S H A R M A ( K C S - 7 1 1 ) compatibility M for o b i transmission le Computing Higher bit rates Novel Spectrum / New frequency bands RAVI SHARMA (KCS-711) Mobile Computing Wider channel bandwidth Upgraded capacity for simultaneous data transfers R AAnytime V I S H A R anywhere M A ( K C S - provisioning 711) Mobile Computing 12 History of Wireless Telephony Standards RAVI SHARMA (KCS-711) Mobile Computing R AFirst Generation (1G) VI SHARMA (KCS-711) Mobile Computing – Signaling: Analog – Multiple Access: FDMA – Introduced In: 1980s RAVI SHARMA (KCS-711) Mobile Computing – Bandwidth: 2.4 Kbps – Communication type: Text, Voice R A V–I Example: SHARMA (KCS-711) Mobile Computing Advanced Mobile Phone System (AMPS) Total Access Communication System (TACS) Nordic Mobile Telephone (NMT) RAVI SHARMA (KCS-711) Mobile Computing – Current Status: Discontinued 13 History of Wireless Telephony Standards RAVI SHARMA (KCS-711) Mobile Computing R ASecond Generation (2G) VI SHARMA (KCS-711) Mobile Computing – Signaling: Digital – Multiple Access: TDMA, CDMA – Introduced In: 1990s RAVI SHARMA (KCS-711) Mobile Computing – Bandwidth: 64 Kbps – Communication type: Text, Voice R A V–I Example: SHARMA (KCS-711) Mobile Computing Global System for Mobile Communication (GSM) , TDMA based Digital Advanced Mobile Phone System (DAMPS), CDMA based Interim Standard 95 (IS-95), CDMA based RAVI SHARMA (KCS-711) Mobile Computing – Current Status: Obsolete 14 History of Wireless Telephony Standards RAVI SHARMA (KCS-711) Mobile Computing R AThird Generation (3G) VI SHARMA (KCS-711) Mobile Computing – Signaling: Digital – Multiple Access: CDMA – Introduced In: 2000s RAVI SHARMA (KCS-711) Mobile Computing – Bandwidth: >2 Mbps – Communication type: Text, Voice ,Video R A V–I Example: SHARMA (KCS-711) Mobile Computing Universal Mobile Telecommunications System (UMTS) CDMA 2000 (IS-2000) R A V–I Current S H A R M Status: A ( K C S Usage -711) declining Mobile Computing 15 History of Wireless Telephony Standards RAVI SHARMA (KCS-711) Mobile Computing R AFourth Generation (4G) VI SHARMA (KCS-711) Mobile Computing – Signaling: Digital – Multiple Access: OFDMA – Introduced In: 2010s RAVI SHARMA (KCS-711) Mobile Computing – Bandwidth: >100 Mbps – Communication type: Text, Voice ,Video R A V–I Example: SHARMA (KCS-711) Mobile Computing Long Term Evolution (LTE) / LTE Advanced / TD-LTE Mobile WiMAX (IEEE 802.16e) WirelessMAN-Advanced (IEEE 802.16m ) RAVI SHARMA (KCS-711) Mobile Computing – Current Status: Ongoing 16 History of Wireless Telephony Standards RAVI SHARMA (KCS-711) Mobile Computing R AFifth Generation (5G) VI SHARMA (KCS-711) Mobile Computing – Signaling: Digital – Multiple Access: OFDMA – Introduced In: 2019 RAVI SHARMA (KCS-711) Mobile Computing – Bandwidth: 10 Gbps – Communication type: Text, Voice ,Video R A V–I Example: SHARMA (KCS-711) Mobile Computing 5G NR (FR1 / FR2) Enhanced Mobile Broadband (eMBB) Ultra Reliable Low Latency Communications (URLLC) RAVI SHARMA (KCS-711) Mobile Computing Massive Machine Type Communications (mMTC) – Current Status: Upcoming 17 RAVI SHARMA (KCS-711) Mobile Computing Cellular RAVI SHARMA (KCS-711) Concept Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 18 Cellular Concept RAVI SHARMA (KCS-711) Mobile Computing RItA is V Ia Ssystem-level H A R M A ( Kidea C S - which 711) calls for replacing M oab isingle, l e C ohigh m p upower ting transmitter (large cell) with many low power transmitters (small cells), each providing coverage to only a small portion of the service area. RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 19 Idea RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing A B C D E F G RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Radio Channels RAVI SHARMA (KCS-711) Mobile Computing 20 Idea RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 21 Idea RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing B B RAVI G C SHARMA (KCS-711) G Mobile Computing C A A RAVI F D SHARMA (KCS-711) FM o b i l e C D omputing E E RAVI SHARMA (KCS-711) Mobile Computing 22 Idea RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing B G C B A G C B F D RAVI SHARMA (KCS-711) A G C Mobile Computing E F D A B E F D G RAVI SHARMA (KCS-711) C B E Mobile Computing A G C F D A E RAVI SHARMA (KCS-711) F D Mobile Computing E 23 Idea RAVI SHARMA (KCS-711) Mobile Computing Each Base Station (BS) is allocated a subgroup of frequency RAVI SHARMA (KCS-711) Mobile Computing channels. Neighboring Base Stations are assigned different channels in order to minimize interference among Base Stations and the mobile RAVI SHARMA (KCS-711) Mobile Computing users under associated to them. By systematically spacing base stations and their channel groups R Athroughout V I S H A R Mthe A ( region, K C S - 7 1the 1 ) available channels M o bmay i l e be C o reused m p u t i nasg many times as necessary so long as the interference between co- channel stations is kept below acceptable levels. RAVI SHARMA (KCS-711) Mobile Computing 24 Advantage RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) D Mobile Computing E F C B E RAVI SHARMA (KCS-711) G Mobile Computing C D A G A F D RAVI SHARMA (KCS-711) B E Mobile Computing F C B G RAVI SHARMA (KCS-711) Mobile Computing Cell Packing: 1. Chang, Hai-Chau, and Lih-Chung Wang. "A simple proof of thue's theorem on circle packing." arXiv preprint arXiv:1009.4322 (2010). 2. Prvan, Marina & Ozegovic, Julije & Burazin Misura, Arijana. (2019). On Calculating the Packing Efficiency for Embedding Hexagonal and Dodecagonal Sensors in a Circular Container. Mathematical Problems in Engineering. 2019. 1-16. 10.1155/2019/9624751. 25 Advantage RAVI SHARMA (KCS-711) Mobile Computing Problem: RAVI SHARMA (KCS-711) Mobile Computing – How to fulfil the increasing demand for service (i.e., as more channels are needed within a region). R ASolution: VI SHARMA (KCS-711) Mobile Computing – Deploy more base stations with lesser transmitter power to avoid added interference). RAVI SHARMA (KCS-711) Mobile Computing Output: – Additional radio capacity with no additional increase in radio spectrum. RAVI SHARMA (KCS-711) Mobile Computing 26 Architecture of a Basic Cellular System RAVI SHARMA (KCS-711) Mobile Computing Base Station RAVI SHARMA (KCS-711) Mobile Computing Base Station RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing R A V I S H A R M A ( K C S - 7MSC 11) PSTN M obile Computing Mobile Switching Center Public Switched Telephone Network 27 Frequency Reuse RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RThe A V Idesign S H A Rprocess M A ( Kof C Sselecting -711) and allocatingMchannel o b i l e groups C o m p for u t iall ng of the cellular base stations within a system is called frequency reuse RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 28 Frequency Reuse: Cellular Coverage RAVI SHARMA (KCS-711) Mobile Computing The actual radio coverage of a cell is known as the footprint and is RAVI SHARMA (KCS-711) Mobile Computing determined by field measurements or propagation prediction models Practically, the footprint of cellular coverage is amorphous 90° RAVI SHARMA (KCS-711) M o b i l e C o m 60° 120° puting 150° 30° RAVI SHARMA (KCS-711) Mobile Computing 180° 0° 210° RAVI SHARMA (KCS-711) M o b i l e C o m p u t i n330° g 240° 300° 29 270° Frequency Reuse: Circle or not? RAVI SHARMA (KCS-711) Mobile Computing A regular shape is required for systematic design of frequency RAVI SHARMA (KCS-711) Mobile Computing reuse plan, overlaid upon a map. It is intuitive to choose circle to represent the coverage area but… R ATo V I cover S H A Ran M area, A ( K Cadjacent S - 7 1 1 ) circles cannot be M overlaid o b i l e C upon o m p ua t map ing without: – Leaving Gaps – Creating overlapping regions RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 30 Frequency Reuse: other shapes? RAVI SHARMA (KCS-711) Mobile Computing What can be that geometric shape that covers an area without gaps and R Aoverlaps? VI SHARMA (KCS-711) Mobile Computing It must be symmetric in shape and size so that it can form a given area homogeneously. RAVI SHARMA (KCS-711) Mobile Computing As each cell represents the footprint of a radiating antenna, assuming the R Aantenna V I S H to A Rbe Mat A the ( K center, CS-7a 1 cell 1 ) must be able to serve M o bthe i l elocation C o mfarthest p u t i n to g its center. For a given distance between the centre of a polygon and its farthest perimeter points, the hexagon has the largest area of the above three. R AHence, V I S Ha A hexagonal R M A ( geometry K C S - 7 1will 1 ) cover any given area M with o b i least l e Ccell o mcount. puting Moreover, hexagon closely approximates a circular radiation pattern which would occur for an omnidirectional base station antenna and free space propagation 31 Frequency Reuse: Allocation RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) 𝑵 M Cells obile Computing 𝑺 Channels (duplex) RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Distributing S channels among N cells such that RAVI SHARMA (KCS-711) Mobile Computing each cell has unique and disjoint channel groups 32 Frequency Reuse: Allocation RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Cells Mobile Computing 1 𝑘 Channels 𝑺 Channels 2 𝑘 Channels RAVI SHARMA (KCS-711) Mobile Computing ⋮ N-1 𝑘 Channels RAVI SHARMA (KCS-711) Mobile Computing N 𝑘 Channels RAVI SHARMA (KCS-711) Mobile Computing 𝑺 = 𝒌𝑵 ,𝑘 < 𝑆 33 Frequency Reuse: Allocation RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Cells 1 2-2.1 GHz RAVI SHARMA (KCS-711) Mobile Computing 2-3 GHz 2 2.15-2.25 GHz ⋮ RAVI SHARMA (KCS-711) Mobile Computing N-1 2.75-2.85 GHz N 2.9-3 GHz RAVI SHARMA (KCS-711) Mobile Computing 34 Frequency Reuse: Reuse factor RAVI SHARMA (KCS-711) Mobile Computing The N cells which collectively use the complete set of available R Afrequencies VI SHARM is Acalled ( K CaScluster. - 7 1 1 )N is called the cluster M o bsize. i l e It Ccommonly o m p u t i has ng the values 4,7,12. If a cluster is replicated M times within the system, the total number of duplex channels (C) can be used as a measure ofMcapacity, RAVI SHARMA (KCS-711) given by: obile Computing 𝐶=𝑀𝑘𝑁=𝑀𝑆 From a design viewpoint, the smallest possible value of N is desirable in order to maximize capacity over a given coverage area. Because, If cluster RAVI SHARMA (KCS-711) Mobile Computing size N is reduced while the cell size is kept constant, more clusters are required to cover a given area, and hence more capacity (a larger value of C) is achieved. R AThe VI SHARMA (KCS-711) Mobile Computing frequency reuse factor of a cellular system is given by 1/N, since each cell within a cluster is only assigned 1/N of the total available channels in the system. 35 Frequency Reuse: Reuse factor RAVI SHARMA (KCS-711) Mobile Computing The value for N is a function of how much interference a mobile or base R Astation V I S H Acan R M Atolerate ( K C S - 7while 1 1 ) maintaining aM osufficient bile Com p u t i nof quality g communications. A large cluster size indicates that the ratio between the cell radius and the R Adistance V I S H Abetween R M A ( co-channel K C S - 7 1 1 cells ) is small. Mobile Computing Conversely, a small cluster size indicates that co-channel cells are located much closer together. RAVI SHARMA (KCS-711) Mobile Computing From a design viewpoint, the smallest possible value of N is desirable in order to maximize capacity over a given coverage area. RAVI SHARMA (KCS-711) Mobile Computing 36 Channel Assignment RAVI SHARMA (KCS-711) Mobile Computing Fixed RAVI SHARMA (KCS-711) Mobile Computing Each cell is allocated a fixed (predetermined) set of voice channels. Any call attempt within the cell can only be served by the unused channels in that particular cell. R AIfV all I the SHAchannels R M A in ( Kthat C S -cell 7 1are 1 ) occupied, the call isMblocked o b i l eand C othe m psubscriber uting does not receive service. Borrowing Strategy: Variation of Fixed RAVI SHARMA (KCS-711) Mobile Computing A cell is allowed to borrow channels from a neighbouring cell if all of its own channels are already occupied. These borrowing procedures are supervised by mobile switching center (MSC) R Asupervises VI SHARMA (KCS-711) Mobile Computing MSC ensures that the borrowing of a channel does not disrupt or interfere with any of the calls in progress in the donor cell 37 Channel Assignment RAVI SHARMA (KCS-711) Mobile Computing Dynamic RAVI SHARMA (KCS-711) Mobile Computing Each time a call request is made, the serving base station requests a channel from the MSC. Then, MSC allocates a channel to the requested cell following an algorithm that RAVI SHARMA (KCS-711) Mobile Computing takes into account: – The likelihood of future blocking within the cell – The frequency of use of the candidate channel RAVI SHARMA (KCS-711) Mobile Computing – The reuse distance of the channel – Other cost functions. Now, MSC allocates a given frequency which is not presently in use in the cell or RAVI SHARMA (KCS-711) Mobile Computing any other cell which falls within the minimum restricted distance of frequency reuse to avoid co-channel interference. 38 Channel Assignment RAVI SHARMA (KCS-711) Mobile Computing Dynamic: R A V I S H A Advantage RMA (KCS-711) Mobile Computing It reduces the likelihood of blocking, which increases the trunking capacity of the system, because all the available channels in a market are accessible to all of the cells. Dynamic: Requirement RAVI SHARMA (KCS-711) Mobile Computing Dynamic channel assignment strategies require the MSC to collect real-time data on: – Channel occupancy – Traffic distribution, and R A V– I Radio S H Asignal R M strength A ( K Cindications S - 7 1 1 )(RSSI) Mobile Computing of all channels on a continuous basis. This increases the storage and computational load on the system but provides the advantage of increased channel utilization and decreased probability of a blocked call. RAVI SHARMA (KCS-711) Mobile Computing Read : http://www.wirelesscommunication.nl/reference/chaptr04/cellplan/dca.htm 39 Handoff / Handover RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Base Station-1 RAVI SHARMA (KCS-711) M o b i l e Base C oStation-2 mputing RAVI SHARMA (KCS-711) Mobile Computing When a mobile moves into a different cell while a conversation is in progress, the R MSC A V I automatically S H A R M A transfers ( K C S - 7the 1 1call ) to a new channelM belonging o b i l e toC the o mnew p u tbase ing station. This transfer of communication and control is termed as Handoff or Handover. 40 Handoff / Handover RAVI SHARMA (KCS-711) Mobile Computing Requirements: RAVI SHARMA (KCS-711) Mobile Computing Identifying a new base station Relocating the voice and control signals to channels of new base stations. RAVI SHARMA (KCS-711) Mobile Computing Expectation: R AHandoff requests are dealt in parallel with VI SHARMA (KCS-711) new call initiation Mobile Computing requests while allocating unused channels. Handoff must be performed successfully and as infrequently as possible R AHandoff V I S H Amust R M Abe( Kimperceptible CS-711) to the usersM o b i l e C o m p u t i n g 41 Handoff / Handover RAVI SHARMA (KCS-711) Mobile Computing Base Station (BS) RAVI SHARMA (KCS-711) Mobile Computing Margin(Δ) = 𝑅𝑆𝑆𝐻𝑇 − 𝑅𝑆𝑆𝐶𝑇 RAVI SHARMA (KCS-711) 𝑹𝑺𝑺𝑯𝑻 M o>b i l 𝑹𝑺𝑺 e Computing 𝑪𝑻 RAVI SHARMA (KCS-711) Mobile Computing RSS Threshold for Handoff Initiation RAVI SHARMA (KCS-711) Minimum M o busable i l e RSS C o for mp acceptable uting Quality of communication * 𝑅𝑆𝑆 (Received Signal Strength) 42 Handoff / Handover RAVI SHARMA (KCS-711) Mobile Computing Considerations: R ASystem V I S designers H A R M Amust ( Kspecify C S - 7an1 optimum 1) RSS at which toMinitiate o b i laehandoff. Computing First, a particular signal strength is specified as the minimum usable RSS for acceptable voice quality at the base station receiver. If Δ is too large, unnecessary handoffs which burden the MSC may occur If Δ is too small, there may be insufficient time to complete a handoff before a call is lost R Adue V I toSweak H A Rsignal M A conditions. (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 𝑹𝑺𝑺 𝑹𝑺𝑺 𝚫 𝚫 RAVI SHARMA (KCS-711) Mobile Computing 𝛿𝑇 𝛿𝑇 𝑻𝒊𝒎𝒆 𝑻𝒊𝒎𝒆 43 Call drop due to Handoff RAVI SHARMA (KCS-711) Mobile Computing R AAV Idropped S H A R M call A ( Kevent C S - 7 1can 1 ) happen when: Mobile Computing 1. There is an excessive delay by the MSC in assigning a handoff. These delays occur due to: R A V I 1. S H AThe RM A network high ( K C S - 7traffic 1 1 ) caused by computational M o b i loading l e C oat mthe p uMSC ting 2. Channel unavailability on any of the nearby base stations 2. The threshold Δ is set too small for the handoff time in the RAVI SHARMA (KCS-711) Mobile Computing system. Vehicle movement v/s Handoff RAVI SHARMA (KCS-711) Mobile Computing 44 Handoff in 1G Systems RAVI SHARMA (KCS-711) Mobile Computing Locator RAVI SHARMA (KCS-711) Mobile Computing Receiver RSS Measurement of users in need of a handoff from the BS neighboring cells. The locator receiver is RAVI SHARMA (KCS-711) M controlled o b i l e Cbyothe m pMSC u t iand n g is used to monitor the signal strength of users in neighbouring cells which appear to be in need of RAVI SHARMA (KCS-711) M handoff o b i l e and C o reports m p u t all i n RSS g values to the MSC. RSS measurement of calls in progress to determine the relative location of each mobile user with respect to the base station RAVI SHARMA (KCS-711) Mobile Computing In first generation analog cellular systems, signal strength measurements are made 45 by the base stations and supervised by the MSC. Handoff in 2G Systems RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing BS-2 BS-1 RAVI SHARMA (KCS-711) Mobile Computing BS-3 RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing In 2G systems, handoff decisions are mobile assisted 46 Handoff in 2G Systems: MAHO RAVI SHARMA (KCS-711) Mobile Computing R Every A V I mobile SHARM station A ( Kmeasures C S - 7 1 1the ) RSS from surrounding M o b i lBSs e Cand o mcontinually puting reports the results of these measurements to the serving BS. A handoff is initiated when the RSS received from the base station of a R neighbouring A V I S H A R cell M A begins ( K C Sto - 7exceed 1 1 ) the power received M o bfrom i l e the C o current m p u t ibase ng station by a certain level or for a certain period of time. The MAHO method enables the call to be handed over between base stations at a RAVI SHARMA (KCS-711) Mobile Computing much faster rate than in first generation analog systems because: The handoff measurements are made by each mobile The MSC no longer constantly monitors signal strengths. RAVI SHARMA (KCS-711) Mobile Computing MAHO is particularly suited for microcellular environments where handoffs are more frequent. 47 Handling Handoff RAVI SHARMA (KCS-711) Mobile Computing R A V I Prioritization S H A R M A ( Kbetween C S - 7 1 1Serving ) M oCall Handoff v/s b i l eInitiation Computing Guard Channel RAVI SHARMA (KCS-711) Mobile Computing A fraction of all available channels in a cell is reserved exclusively for handoff requests from on-going calls which may be handed off into the cell. RAVI SHARMA (KCS-711) Mobile Computing Queuing Queuing of handoffs is possible due to the fact that there is a finite value of Δ = 𝑅𝑆𝑆𝐻𝑇 − 𝑅𝑆𝑆𝐶𝑇. The delay time and size of the queue is determined from the traffic pattern of the particular RAVI SHARMA (KCS-711) Mobile Computing service area. 48 Handling Handoff RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Guard Channel Queuing It does not guarantee a zero probability It has the disadvantage of reducing the Rtotal A V Icarried S H A traffic, R M A as ( Kfewer C S - 7channels 11) of forced termination, M o b i l esince Com large p u delays ting will cause the 𝑹𝑺𝑺 to drop below the are allocated to originating calls. 𝑹𝑺𝑺𝑪𝑻 and lead to forced termination. RAVI SHARMA (KCS-711) Mobile Computing It decreases the probability of forced It offers efficient spectrum utilization termination of a call due to lack of when dynamic channel assignment available channels. There is a trade-off strategies, which minimize the number between the decrease in probability of RofA required V I S H Aguard R M Achannels ( K C S by - 7 efficient 11) M o b i l and forced termination e C ototal m p ucarried ting demand-based allocation, are used. traffic. 49 Practical Handoff Considerations RAVI SHARMA (KCS-711) Mobile Computing Umbrella Cell RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Micro Cell RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Umbrella cell for High speed traffic Micro Cell for Low speed traffic 50 Exercise RAVI SHARMA (KCS-711) Mobile Computing 1. Can you identify a simplex and half duplex communication system as seen in real life? RAVI SHARMA (KCS-711) Mobile Computing 2. What is the dwell time in a cellular communication? 3. What do we mean by Intersystem handoff? 4. What is the cell dragging problem with the handoffs in umbrella cell approach? R A VWhat 5. I S isHthe M A 𝚫( Kvalue A Rtypical C S for - 7 different 11) M o bsystems? generations of cellular ile Computing 6. What is the improvement (over the cellular generation) in “time required to perform handoff” after the decision on a suitable handoff cell has been made? R A VWhat 7. I S isHhard ARM andAsoft ( Khandoffs? CS-711) Mobile Computing 8. Name any other metric other than RSS that is utilized for making handoff decisions in newer cellular systems. 9. R A VRead I S about H A R the M Afollowing ( K C S -techniques 711) utilized for increasing M o bthe i l ecapacity C o mofp ua tcellular ing system: 1) Cell Splitting 2) Sectoring 51 RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing 52 GSM: History RAVI SHARMA (KCS-711) Mobile Computing GSM was originally developed to serve as a PAN-European cellular service. RAVI SHARMA (KCS-711) Mobile Computing – 1983: Groupe Spécial Mobile – 1992: Global System for Mobile Communications The GSM standard was developed by European Telecommunications R AStandards V I S H A RInstitute M A ( K(ETSI). CS-711) Mobile Computing Most GSM systems primarily operated in 900 or 1800 MHz bands (secondary: 850 and 1900 MHZ). RAVI SHARMA (KCS-711) Mobile Computing GSM is an obsolete technology and its decommissioning across all different geographical regions started with Telstra in Australia on 1st December 2016. R AItV isI aS Hsecond-generation A R M A ( K C S - 7(2G) 1 1 ) standard employing M o time-division b i l e C o m pmultiple- uting access (TDMA) spectrum-sharing. 53 GSM: Services RAVI SHARMA (KCS-711) Mobile Computing GSM services follow ISDN* guidelines RAVI SHARMA (KCS-711) Mobile Computing * Telephone Services Integrated Offered by a mobile service provider to a caller Services Digital R A V I S H A R M Voice A call, ( K Cfax, S -SMS, 7 1 1MMS, ) Emergency Number M o b i l e C o m p Network uting Bearer/Data Services Limited to Layer 1,2,3 of the OSI reference model R A V I S H A R M Provides A ( K data C S -transmission 711) service Mobile Computing Circuit Switched (CSD / HSCSD), Packet Switched (GPRS) Supplementary Services R A V I S H A R CallA forwarding, M ( K C S - 7barring, 1 1 ) waiting, hold, conferencing Mobile Computing Calling Line Identification Presentation (CLIP)/ Restriction (CLIR) Closed User Group (CUG), Advice of Charge (AoC) Unstructured supplementary services data (USSD) 54 GSM: Process RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing BSC Base Station R A VMS/UE I SHARMA (KCS-711) Mobile Computing Controller BTS Mobile Station / User Equipment Base Transceiver Station RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing PSTN MSC 55 GSM: Interfaces RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Abis Interface SS7 MS BTS BSC MSC PSTN RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing R A V Air I SInterface HARMA (KCS-711) A Interface Mobile Computing (GSM Radio) 56 RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing GSM Subsystems RAVI SHARMA (KCS-711) Mobile Computing Base Station Network Switching Operation Support R A V I Subsystems SHARMA ( K C S - 7 1 1 Subsystem ) M o b i l Subsystem e Computing (BSS) (NSS) (OSS) RAVI SHARMA (KCS-711) Mobile Computing 57 GSM Subsystems: Base Station RAVI SHARMA (KCS-711) Mobile Computing R A Mobile V I S HStation A R M A ( K CBase S - 7Transceiver 11) System M Base o b i Station l e C o Controller mputing (MS) (BTS) (BSC) RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Base Station Subsystem (BSS) 58 GSM: BSS RAVI SHARMA (KCS-711) Mobile Computing Also, known as Radio Subsystem provides and manages radio RAVI SHARMA (KCS-711) Mobile Computing transmissions between MS and MSC MSs communicate to BSS over Air interface R ABSS V I Sconsists H A R M of A (many K C S - BSCs 7 1 1 )which connects to M osingle b i l e MSC. C o m pEach u t i nBSc g typically controls several hundred BTSs BTSs may be co-located at the BSCs while others can be distributed R Aremotely V I S H A having R M A microwave ( K C S - 7 1 link 1 ) or dedicated leased Mob ile Computing lines. Mobile handoffs between two BTSs (under the control of same BSC) are handled by BSC (in-turn reducing the switching burden of the MSC). RAVI SHARMA (KCS-711) Mobile Computing BSCs are physically connected to the MSC via dedicated/leased lines or 59 microwave links. GSM: System Architecture RAVI SHARMA (KCS-711) Mobile Computing R A V I S H A R M ABTS( K C S - 7 1 1 ) Mobile Computing MS BTS BSC R A V I S H A R M ABTS( K C S - 7 1 1 ) Mobile Computing PSTN MSC ISDN RAVI SHARMA (KCS-711) Mobile Computing Data BTS Networks MS BTS BSC RAVI SHARMA (KCS-711) Mobile Computing BTS 60 GSM: NSS RAVI SHARMA (KCS-711) Mobile Computing NSS handles the switching of GSM calls between external networks R Aand V I the S H ABSCs R M Ain (the K C BSS. S-711) Mobile Computing It is also responsible for managing and providing access to several customer databases namely: – Home Location Register (HLR) R A V I S HIt Acontains R M A the ( K subscriber C S - 7 1 1and ) location information M for o b each i l e user C o who m p resides u t i n gin the same city as the MSC. Each subscriber in a particular GSM market is assigned a unique International Mobile Subscriber Identity (IMSI) number used to identify each home user. R A V–I Visitor S H A RLocation M A ( K CRegister S - 7 1 1 )(VLR) Mobile Computing It temporarily stores the IMSI and customer information for each roaming subscriber who is visiting the coverage area of a particular MSC. VLR is linked between adjacent MSCs in a particular market/geographical region R A V I S Hand A Rcontains M A (subscription K C S - 7 1 1information ) of every visiting M o user b i l in e the C oarea. mputing Once the roaming mobile is logged in the VLR, the MSC sends the necessary information to the visiting subscriber’s HLR so that call to the roaming mobile can be appropriately routed over the PSTN by roaming user’s HLR 61 GSM: NSS RAVI SHARMA (KCS-711) Mobile Computing – Authentication Center (AUC) R A V I S HItAisRaMstrongly A ( K Cprotected S - 7 1 1 )database which handles M o bthe i l eauthentication C o m p u t i nand g encryption keys for every single subscriber in the HLR and VLR. It contains a register called the Equipment Identity Register (EIR) which identifies stolen or fraudulently altered phones that transmit identity data transmit identity data that doesn’t match the information contained in RAVI SHARMA (KCS-711) Mobile Computing either the HLR or VLR. HLR VLR AUC BTS R A VMS I S H A R BTS M A ( K C S - 7 BSC 11) M o b i l e C o mPSTN puting BTS MSC ISDN BTS RAVI SHARMA (KCS-711) M o b i l e C o m p Data uting MS BTS BSC Networks BTS 62 GSM: OSS RAVI SHARMA (KCS-711) Mobile Computing It supports one or more Operation Maintenance Centers (OMCs) R Awhich V I S Hare A R used M A ( to K Cmonitor S - 7 1 1 ) and maintain the M operformance b i l e C o m p of u t each ing MS, BS, BSC and MSC. It has 3 main functions: RAVI SHARMA (KCS-711) Mobile Computing – Maintenance of all Telecommunication H/W and network operations with a particular market – Management of all charging and billing procedures – Management of all mobile equipment in the system. RAVI SHARMA (KCS-711) Mobile Computing OMC also has provisions for: – Adjusting BS parameters and billing procedures R A V– I Providing S H A R Msystem A ( K Coperators S - 7 1 1 )the ability to determine M o b ithe l e performance C o m p u t i nand g integrity of each Subscriber equipment within the system. 63 GSM: OSS RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing HLR VLR AUC BTS MS BTS RAVI SHARMA (KCS-711) BSC M o b i l e C o mPSTN puting BTS MSC ISDN BTS RAVI SHARMA (KCS-711) M o b i l e C o m p Data uting MS BTS BSC Networks BTS RAVI SHARMA (KCS-711) OSSM o b i l e Computing 64 GSM: Channel Types RAVI SHARMA (KCS-711) Mobile Computing There are two types of GSM logical channels: R A V– I Traffic S H A Channels R M A ( (TCHs) KCS-711) Mobile Computing – Control Channels (CCHs) TCHs carry digitally encoded user speech or user data and have RAVI SHARMA (KCS-711) Mobile Computing identical functions and formats on both the forwards and reverse link. R ACCHs VI SHcarry A R Msignaling A ( K C S and - 7 1 1synchronizing ) commands M o b i l ebetween C o m p uthe t i nBS g and the mobile station R AFor further subdivision, read at: VI SHARMA (KCS-711) Mobile Computing https://www.ecstuff4u.com/2018/02/gsm-channel-types.html 65 GPRS: General Packet Radio Service RAVI SHARMA (KCS-711) Mobile Computing RAVI SHARMA (KCS-711) Mobile Computing Data Communication Standards (Internet Access) RAVI SHARMA (KCS-711) Mobile Computing HSCSD EDGE GPRS R A V I S H A R M A ( K C S - 7 1 1(High ) Speed M o b(Enhanced i l e C o m pData uting (General Packet Circuit Switched Rates for Global Radio Service) Data) Evolution RAVI SHARMA (KCS-711) Mobile Computing 66 GPRS: General Packet Radio Service RAVI SHARMA (KCS-711) Mobile Computing It is a packet based data network standard and was originally designed to provide R Apacket VI SH data A Raccess M A (for K CGSM S - 7network. 11) It later expanded M over o b i IS-136. le Computing Suitable for non-real time internet usage, e.g. – Email access, Fax – Asymmetric (more download, less upload) Web browsing RAVI SHARMA (KCS-711) Mobile Computing GPRS supports multi user network sharing of individual radio channels and time slots. An individual GPRS user can achieve a maximum of 172.2 Kbps (8 time slots of R A21.4 V I Kbps) SHARMA (KCS-711) Mobile Computing Data throughput experienced by a GPRS user decreases substantially with simultaneously usage attempts by other users. R AImplementation V I S H A R M Aof (GPRS K C S merely - 7 1 1 requires ) the GSM operator M o b i to l e install C o mnew p u routers ting and internet gateways at BS along with a software that redefines BS air interface standard for GPRS channels and time slots. – No new BS RF hardware is required. 67
