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Cellular Concept and Frequency Reuse
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Cellular Concept and Frequency Reuse

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Questions and Answers

What is the formula used to calculate the total number of cells N in a cluster design?

  • N = i^3 + j^3
  • N = i^2 + ij + j^2 (correct)
  • N = i^2 + j^2 + 2ij
  • N = i + j + ij

    • In fixed channel assignments, what happens when all channels in a cell are occupied?

  • The call is blocked. (correct)
  • The call is placed on hold until a channel is free.
  • The call is rerouted to another cell.
  • The call receives a priority queue for the next available channel.

    • Which strategy allows a cell to borrow channels from neighboring cells when needed?

  • Fixed Channel Assignments (correct)
  • Adaptive Channel Assignments
  • Dynamic Channel Assignments
  • Borrowing Strategy

    • What is the role of the Mobile Switch Center (MSC) in channel assignment strategies?

    <p>To connect cells to the wide area network and manage call setup.</p> Signup and view all the answers

    What does the formula N = i^2 + ij + j^2 imply about the values of i and j?

    <p>i and j are non-negative integers.</p> Signup and view all the answers

    What characterizes a soft handoff in CDMA systems?

    <p>The mobile unit has simultaneous radio links with more than one base station.</p> Signup and view all the answers

    What is the purpose of reserving guard channels in a cellular system?

    <p>To ensure that at least some channels are available for handoffs.</p> Signup and view all the answers

    Which type of interference occurs with cells that use the same set of frequencies?

    <p>Co-channel interference.</p> Signup and view all the answers

    What is the primary tradeoff when queuing handoff requests?

    <p>Network traffic versus the likelihood of call drops.</p> Signup and view all the answers

    What effect does co-channel interference have on voice channels?

    <p>Crosstalk that affects the call quality.</p> Signup and view all the answers

    What is a key reason for performing a handover in a cellular radio system?

    <p>To move out of the cell’s coverage area</p> Signup and view all the answers

    Which type of handover requires the mobile device to actively measure and report signal strength?

    <p>Mobile Assisted Handoff</p> Signup and view all the answers

    What is the consequence of having the handoff threshold ($\Delta$) set too small?

    <p>Calls will be dropped frequently.</p> Signup and view all the answers

    In a hard handoff, which statement is true about the connection with the base stations?

    <p>The connection is terminated with the old base station before establishing a connection with the new one.</p> Signup and view all the answers

    What is a primary disadvantage of using a Network Controlled Handoff?

    <p>It imposes a significant burden on the Mobile Switching Center (MSC).</p> Signup and view all the answers

    What is the main characteristic of intra-cell handover?

    <p>It involves changing the frequency within the same cell.</p> Signup and view all the answers

    During an inter-BSC, intra-MSC handover, what is the primary factor in the transition?

    <p>The handover involves changing BSCs while staying within the same MSC.</p> Signup and view all the answers

    What is a significant challenge in executing a handover in cellular systems?

    <p>It needs to be completed before the user notices.</p> Signup and view all the answers

    What was a major limitation of the first mobile radio-telephone services?

    <p>A lot of bandwidth was dedicated to a single call.</p> Signup and view all the answers

    What organization approved the cellular concept proposed by Bell Labs?

    <p>FCC</p> Signup and view all the answers

    What geometric shape is typically used to represent the coverage area of a cell in a cellular network?

    <p>Hexagon</p> Signup and view all the answers

    What is the impact of smaller cell sizes on cellular networks?

    <p>They allow for higher channel capacity.</p> Signup and view all the answers

    In frequency reuse, what is the goal regarding adjacent cells?

    <p>To use different frequencies to avoid interference.</p> Signup and view all the answers

    What occurs when the cluster size N is large in a cellular network?

    <p>Weaker interference and lower capacity.</p> Signup and view all the answers

    What defines the frequency reuse factor in a cellular network?

    <p>The ratio of frequency channels used per cluster.</p> Signup and view all the answers

    When more base stations are added to a cellular network, what is a potential downside?

    <p>More frequent handoffs.</p> Signup and view all the answers

    What does the total number of channels that can be used in a system depend on?

    <p>The number of clusters and channels per cell.</p> Signup and view all the answers

    Which of the following statements is true about the allocation of channels in a cellular system?

    <p>Cells are assigned specific groups of channels to minimize interference.</p> Signup and view all the answers

    What does a small co-channel reuse ratio (Q) indicate about the cluster size and capacity?

    <p>Small cluster size and high capacity</p> Signup and view all the answers

    Which formula represents the co-channel reuse ratio?

    <p>Q = sqrt(3N)</p> Signup and view all the answers

    What tradeoff must be made in actual cellular design?

    <p>Capacity vs. cluster size</p> Signup and view all the answers

    For a system with a high co-channel reuse ratio, what effect can be expected on transmission quality?

    <p>Transmission quality would be improved</p> Signup and view all the answers

    In terms of interference, what does S/I approximately equal to?

    <p>R^4 / [2(D-R)^4 + 2(D+R)^4 + 2D^4]</p> Signup and view all the answers

    What factor can lead to adjacent channel interference?

    <p>Imperfect receiver filters</p> Signup and view all the answers

    In the context of cellular networks, which parameter affects the signal-to-interference-plus-noise ratio (SINR)?

    <p>Factor of the propagation constant</p> Signup and view all the answers

    What is the relationship between the reuse factor and the required cluster size in cellular design?

    <p>The reuse factor increases with smaller cluster sizes</p> Signup and view all the answers

    Study Notes

    Cellular Concept

    • Cellular concept was proposed in 1968 by Bell Labs to the FCC
    • The concept divides coverage areas into cells, each served by a base station with a lower power transmitter
    • Cells typically span a few hundred meters in cities and 10s of kilometers in rural areas
    • Each cell is assigned a portion of the available channels and neighboring cells are assigned different frequency groups to minimize interference
    • The hexagonal geometry provides optimal cell shape for coverage

    Frequency Reuse

    • Adjacent cells are assigned different frequencies to avoid interference
    • 10 to 50 frequencies are assigned to each cell with controlled transmission power to limit inter-cell interference
    • The cluster size (number of cells with unique frequency groups) is typically 4, 7, or 12
    • Increasing cluster size reduces interference but lowers capacity, while a smaller cluster size offers higher capacity with increased interference
    • The frequency reuse factor, 1/N, determines the portion of total channels assigned to each cell within a cluster

    Channel Assignment Strategies

    • Fixed channel assignments allocate a predetermined set of voice channels to each cell, potentially leading to call blocking and subscriber service interruptions
    • Dynamic channel assignments dynamically allocate channels based on real-time conditions, reducing the likelihood of blocking but increasing complexity

    Handoff

    • Handoff is the process of transferring an ongoing call from one base station to another
    • Handoff scenarios include intra-cell (frequency changes), inter-cell (movement across cells), and inter-MSC (movement across mobile switching centers)
    • Handoff must be seamless, infrequent, and imperceptible to users

    Types of Handoff

    • Hard handoff breaks the existing connection before establishing a new one, common in FDMA and TDMA systems
    • Soft handoff maintains simultaneous connections with multiple base stations during transfer, characteristic of CDMA systems
    • Vertical handoff involves transitioning between different network technologies, potentially from a cellular to a Wi-Fi network

    Prioritizing Handoffs

    • Call dropping is more disruptive than busy lines, so handoffs are prioritized to minimize call interruptions
    • Guard channel concept reserves channels for handoffs, but it consumes bandwidth
    • Queuing handoff requests allows managing handoff requests, balancing call dropping probability and network traffic

    Interference and System Capacity

    • Interference is a major limiting factor in cellular network performance
    • Sources of interference include other mobiles, neighboring calls, other base stations, and non-cellular systems operating in the same frequency band
    • Co-channel interference occurs between cells using the same frequencies
    • Adjacent channel interference results from signals close in frequency to the desired signal due to imperfect receiver filters

    Co-channel Reuse Ratio

    • The co-channel reuse ratio (Q) measures the distance between nearest co-channel cells relative to cell radius
    • A smaller Q leads to a smaller cluster size (N) and higher capacity, while a larger Q improves transmission quality
    • Balancing capacity and transmission quality is key in cellular network design

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    Related Documents

    Cellular Concept PDF

    Description

    Explore the principles of the cellular concept proposed by Bell Labs, which revolutionized communication by dividing coverage areas into cells. This quiz covers the mechanics of frequency reuse, the impact of cluster size, and how these concepts minimize interference for optimal communication efficiency.

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