logging in or signing up COCHANNEL INTERFERENCE REDUCTION IN GSM anusha99 Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 281 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: February 22, 2011 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript COCHANNEL INTERFERENCE REDUCTION IN GSM: COCHANNEL INTERFERENCE REDUCTION IN GSM Ramhari Bhapkar Anup Gholkar Abhijeet Kumbhojkar Introduction to Cellular Systems: Solves the problem of spectral congestion and user capacity. Offer very high capacity in a limited spectrum without major technological changes. Reuse of radio channel in different cells. Enable a fix number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region. Introduction to Cellular SystemsFrequency Reuse: Each cellular base station is allocated a group of radio channels within a small geographic area called a cell. Neighbouring cells are assigned different channel groups. By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells. Keep interference levels within tolerable limits. Frequency reuse or frequency planning seven groups of channel from A to G Frequency ReuseFrequency Reuse: Frequency ReuseSlide 5: Co-channel Interference and System Capacity To reduce co-channel interference, co-channel cell must be separated by a minimum distance. When the size of the cell is approximately the same co-channel interference is independent of the transmitted power co-channel interference is a function of R: Radius of the cell D: distance to the centre of the nearest co-channel cellSlide 6: For a hexagonal geometry Q = D/R = √3N A small value of Q provides large capacity A large value of Q improves the transmission quality - smaller level of co-channel interference A trade-off must be made between these two objectivesImproving Capacity in Cellular System: Methods for improving capacity in cellular systems – Cell Splitting: subdividing a congested cell into smaller cells. – Sectoring: directional antennas to control the interference and frequency reuse . Improving Capacity in Cellular SystemReducing cochannel interference: Increasing the separation between two cochannel cells Using directional antennas at the base station lowering the antenna heights at the base station . The use of directional antennas in each cell can serve two purposes : - further reduction of cochannel interference - increasing the channel capacity when the traffic increases. Reducing cochannel interferenceCell Sectoring: Decrease the co-channel interference and keep the cell radius R unchanged – Replacing single omni-directional antenna by several directional antennas – Radiating within a specified sector Cell SectoringCell Sectoring: Cell SectoringCause of Cochannel Interference in sectored antenna: Cause of Cochannel Interference in sectored antennaNotch in sectored antenna: The interfering site could cause interference at those cells within a 19◦ sector in front of the cell. In an ideal situation the antenna pattern of the serving cell must be rotated clockwise by 10◦ such that the notch can be aimed properly at the interfering cell Notch in sectored antennaNotch in sectored antenna: Notch in sectored antennaTypes of tilting: Purely mechanical tilt Fixed electrical tilt variable electrical tilt (VET) Remote electrical tilt (RET) Continuously adjustable electrical downtilt (CAEDT). Types of tiltingDowntilting: DowntiltingPhase shifting network in electrical tilting: Phase shifting network in electrical tiltingVertical antenna pattern: Vertical antenna patternHorizontal antenna pattern: Horizontal antenna patternCautions in Tilting Antennas: Elements playing a major role in justifying antenna tilting- The antenna vertical pattern The antenna height Cautions in Tilting AntennasUmbrella pattern: For controlling the energy in a confined area, the umbrella-pattern antenna can be developed by using a monopole with a top disk The size of the disk determines the tilting angle of the pattern. The smaller the disk, the larger the tilting angle of the umbrella pattern. Umbrella patternUmbrella pattern: Umbrella patternBenefits of umbrella pattern: Energy is confined to the immediate area of the antenna Reduces cochannel and long-distance interference. We can increase antenna height still reduce cochannel interference The frequency-reuse distance can be shortened Benefits of umbrella patternMicrocell Zone Concept: • Antennas are placed at the outer edges of the cell • Any channel may be assigned to any zone by the base station • Mobile is served by the zone with the strongest signal. • Handoff within a cell – No channel reassignment – Switch the channel to a different zone site Reduce interference – Low power transmitters are employed Microcell Zone ConceptMicrocell Zone Concept: Microcell Zone ConceptPower control for reducing interference: Ensure each mobile transmits the smallest power necessary to maintain a good quality link on the reverse channel Can be controlled only by mobile station – long battery life – increase SIR Power control for reducing interferenceUse of Parasitic element: Creating a desired pattern in a certain direction. currents appearing in several parasitic antennas are caused by radiation from a nearby drive antenna . Ways to combine a driven antenna & a single parasite : - Normal spacing - Close spacing Use of Parasitic elementNormal spacing: a)One-quarter wavelength spacing b) one-half wavelength spacing c) combination of a and b. Normal spacingClose spacing: Length of both elements same - Forms a null at the centre - D irective gain of 3 dB relative to a single element Length of parasite greater than active element - Parasite acts as reflector - D irective gain of 6 dB Length of parasite less than active element - Parasite acts as director - D irective gain of 8 dB Close spacingClose spacing: Close spacingJOINT DEMODULATION OF CO CHANNEL SIGNALS: JOINT DEMODULATION OF CO CHANNEL SIGNALS Dominant interfererence likely exists in GSM Number of nearby co channel interference is rather small Cancellation of it can improve the receiver performance It depends on the dominant to rest of interference ratio DIR.JOINT DEMODULATION OF CO CHANNEL SIGNALS: Receiver algorithm identifies dominant interfering signal It removes it by joint phase demodulation System performance improves by 1.3 dB JOINT DEMODULATION OF CO CHANNEL SIGNALSThank You: Thank You You do not have the permission to view this presentation. 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