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Date added: 16 June 2020
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  • W-CDMA seems to be the BIG rage nowadays!
  • The Third Generation Mobile System is the future
    mobile communication technology that carries
    existing and future services on a unified
    platform. W-CDMA is a prominent step in this
    direction. Killer Wireless Application or not,
    W-CDMA is being adopted in more and more
    countries and is becoming one of the leading
    Wireless Standards in the World.
  • Wideband Code division Multiple Access (W-CDMA)
    is a "spread spectrum" technology, which means
    that it spreads the information contained in a
    particular signal of interest over a much greater
    bandwidth than the original signal. WCDMA makes
    very efficient use of the available radio
    spectrum. No frequency planning is needed, since
    one-cell re-use is applied.

  • WCDMA a 3rd-generation mobile services platform
    is based on modern, layered network-protocol
    structure, similar to the protocol structure used
    in GSM networks and CDMA. But it has got many
    advanced features owing to its wider bandwidth
    and more enhanced capability to use whole
    available spectrum which consequently increases
    security features in the technology. The coded
    data is more secured and transmitted at a higher
  • The intent of this paper is to provide insight
    into the technology of WCDMA and to describe some
    of the operating features of the proposed W-CDMA
    system which also includes coding of data, modes
    of transmission of data and briefly discusses how
    the data is transmitted. The paper also
    highlights upon the actual communication done on
    mobile phones. The paper is concluded by giving
    the benefits and applications of W-CDMA.

  • The power of information
    is limitless. The way to tap into this source of
    great power is through effective communication --
    in business as well as in the more personal
    dimension of our lives. However, the world of
    today is a place where we can no longer afford to
    remain stationary in order to provide or obtain
    information. We must constantly be "in touch", no
    matter where we may be. We are witnessing the
    dawning of a new age the age of mobile
  • The following figure shows the comparison
    between the present day radio cell structure
    compared to the radio cells that will be used in
    the W-CDMA system. Uplink and downlink capacity
    can be adjusted according to needs.
  • GSM and similar ABC
  • F1 F2
    Each cell corresponds to ABC
  • The W-CDMA systems employs transmission power
    control, diversity reception and an error control
    scheme capable of following the time variations
    in the radio propagation circuit in order to
    maintain high speech quality in poor radio
    propagation circuits and adopts a noise robust
    voice coding methods. To achieve high system
    capacity, a spectrum spreading modulation/demodula
    tion method which is robust to interference noise
    and an efficient interference cancellation system
    are adopted.

  • Spread spectrum
  • W-CDMA is a "spread
    spectrum" technology, which means that it spreads
    the information contained in a particular signal
    of interest over a much greater bandwidth than
    the original signal.
  • The initial data is
    "spread," including the application of digital
    codes to the data bits. The data bits of each
    call are then transmitted in combination with the
    data bits of all of the calls in the cell. At the
    receiving end, the digital codes are separated
    out, leaving only the original information which
    was to be communicated. At that point, each call
    is once again a unique data stream.
  • Traditional uses of spread
    spectrum are in military operations. Because of
    the wide bandwidth of a spread spectrum signal,
    it is very difficult to jam, difficult to
    interfere with, and difficult to identify. This
    is in contrast to technologies using a narrower
    bandwidth of frequencies. Since a wideband spread
    spectrum signal is very hard to detect, it
    appears as nothing more than a slight rise in the
    "noise floor" or interference level. With other
    technologies, the power of the signal is
    concentrated in a narrower band, which makes it
    easier to detect.

  • In the standard, the
    mobile device is referred to as User Equipment
    (UE), which means a mobile device and multimedia
    terminal that takes care of voice (basically like
    a mobile phone) as well as transferring pictures
    and video.
  • On the terminal side, the
    UE is a mobile device that could contain a
    variety of functions and not necessarily an
    ordinary mobile phone. On the infrastructure
    side, the UE is communicating with the Node B
    the base station. In the next instance, Node Bs
    are communicating with the Radio Network
    Controller (RNC). The Mobile Switching Center is
    shared among all connected networks.

  • The radio interface consists of three layers,
    each of which provides services with specific
    tasks and functions. The Radio Interface protocol
    is divided into
  • Physical Layer (Layer 1)
  • Data Link Layer (Layer 2)
  • Network Layer (Layer 3)
  • The Data Link Layer, in turn, consists of four
  • Media Access Control (MAC)
  • Radio Link Control (RLC)
  • Packet Data Convergence Protocol (PDCP) and
  • Broadcast Multicast Control (BMC).
  • Finally the Network Layer consists of the Radio
    Resource Control (RRC). All information is passed
    between the layers via channels (CH) or Service
    Access Points (SAP). SAP provides services for
    the upper layers or the application. A SAP
    comprises a set of operations for

  • the upper layers to fulfill specific commissions.
    SAP are divided into control and traffic SAPs,
    with the control SAPs carrying control
    information and the traffic SAPs passing the user
  • Channels are defined between the lower layers in
    the protocol-
  • Physical Layer
  • Media Access Control Layer
  • Radio Link Control.
  • The logical channels are describing what type of
    data is transported, control information or
    traffic data. The transport channels are
    characterized by how the data is transferred-
    Common or Dedicated. If the data is transferred
    through the common channel, the data is
    distributed to several receivers in a cell and
    correspondingly, data on the dedicated channel is
    distributed to a specific receiver.

  • Physical Layer
  • The physical layer
    continuously measures power on the physical
    channel to keep track of necessary weighting of
    the transmitted power, and to maximize the
    efficiency in the air. The physical layer is
    controlled by RRC. Other commissions for physical
    layer include mapping the information between the
    transport channels and physical channels.
  • The Physical layer
    includes the variable bit rate transport channels
    required for Bandwidth-on-demand user
    applications. These can multiplex several
    services onto a single connection between the
    fixed infrastructure and a mobile terminal. Some
    of the physical channels do not carry transport
    channels in fact, they do not carry user
    information of any kind. They serve the physical
    layer itself, and include such resources as some
    pilot channels (that assist in modulation
    recovery), a synchronization channel (that lets
    mobile terminals synchronize to the network),
    paging channel and traffic channels.

  • The Pilot Channel is used by the mobile unit to
    obtain initial system synchronization and to
    provide time, frequency, and phase tracking of
    signals from the cell site. Synchronization
    channel provides cell site identification, pilot
    transmit power, and the cell site pilot
    pseudo-random (PN) phase offset information. With
    this information the mobile units can establish
    the System Time as well as the proper transmit
    power level to use to initiate a call. The mobile
    unit will begin monitoring the paging channel
    after it has set its timing to the System Time
    provided by the sync channel. Once a mobile unit
    has been paged and acknowledges that page, call
    setup and traffic channel assignment information
    is then passed on the paging channel to the
    mobile unit. Traffic channel carries the actual
    phone call and carries the voice and mobile power
    control information from the base station to the
    mobile unit.

  • Medium Access Control Layer
  • The main function of the
    MAC layer is to map the control information and
    user traffic to different channels provided by
    the physical layer, the logical channels to
    transport channels. Control channels pass control
    information while traffic channels contain user
    information. Mac provides the two categories of
    logical channels to the RLC layer.

  • Radio Link Control
  • The main task of the RLC
    layer is to transfer user data and provide the
    necessary quality of service (QoS) depending on
    the application and degree of insurance that the
    data will be transmitted to the peer. The RLC
    takes care of error correction and retransmission
    as well as the segmenting and reassembling of
    data. Retransmission is used when an
    unrecoverable error has occurred, and it is
    controlled by the RRC to provide different levels
    of QoS.
  • Packet Data Convergence Protocol
  • PDCP Layer provides
    support for network layer protocols such as IPv4
    and IPv6. The PDCP also handles functions such as
    header compression and decompression for TCP/IP
    packets to improve the data throughput and
    performance on the channels. The RRC controls
    which compression algorithm is to be used.
  • Broadcast Multicast Control
  • The requirements to get
    point-to-multipoint services for the protocol are
    fulfilled with the BMC Layer. Data is sent
    unacknowledged and delivery of information is not

  • Broadcast Multicast Control
  • The requirements to get
    point-to-multipoint services for the protocol are
    fulfilled with the BMC Layer. Data is sent
    unacknowledged and delivery of information is not
  • Radio Resource Control
  • By far, the most complex
    and the largest layer in the radio interface
    protocol is RRC because of wide range of
    functions delivered and provided. The main tasks
    are to establish, maintain, and release a
    connection. However, the RRC also controls
    several other essential SAP functions. The other
    functions taken care of by the RRC includes
    establishing and maintaining required QoS for a
    connection. This implies the controlling of the
    other layers and accomplishes right decisions out
    of reported/collected connection statistics and

  • How The Data is Coded ?
  • With W-CDMA, a user's
    information bits are spread over an artificially
    broadened bandwidth. The job is done by
    multiplying them with a pseudorandom bit stream
    running several times as fast. The bits in the
    pseudorandom bit stream are referred to as chips,
    so the stream is known as a chipping, or
    spreading, code. It increases the bit-rate of the
    signal (and the amount of bandwidth it occupies)
    by a ratio known as the spreading factor, namely,
    the ratio of the chip rate to the original
    information rate.
  • Lets look into the matter,
    now! In the case of Downlink, voice data is first
    passed through a Convolutional Encoder which
    doubles the data rate. It is then interleaved, a
    process that has no effect on the rate but does
    introduce time delays in the final construction
    of the signal. A long code is Ex-ored with the
    data which is a voice privacy function and not
    needed for channelization. W-CDMA then applies a
    64-bit Walsh code which is uniquely assigned to a
    base to mobile link to form one channel which
    sets a physical limit of 64 channels on the
    forward link. And these channel include Pilot
    channel, Synchronization channel, Paging channel
    and Traffic channel. In the final stages of the
    encoding, a Psuedo-Random code is added to the
    signal that repeats itself after a finite amount
    of time, which results in the spreading of the

  • Walsh code
  • Walsh codes have the
    characteristics of being orthogonal to each other
    and to the logical Not of each other. They are
    generated by the recursive expansion of the Walsh
    function shown below
  • w2n wn wn
  • wn wn
  • These codes are used on
    the forward link for channel separation. In a
    code division system, one user's call is
    separated from another users call by the
    application of this Walsh Code. On the reverse
    link, Walsh Codes are used to modulate the data.
  • bits capable of producing 4.4 trillion
    combinations of code. The code is so long in fact
    that it takes 41 days before the code begins to
    repeat itself.

  • Two duplex modes of transmission have been
  • Time Division Duplex (TDD).

  • Frequency Division Duplex (FDD).
  • In FDD mode, a physical channel is
    characterized by the code, frequency, and in the
    Uplink (the relative phase). FDD employs separate
    uplink and downlink frequency bands with a
    constant frequency offset between them. The other
    form, TDD, puts the uplink and the downlink in
    the same band, and then time-shares transmissions
    in each direction. This mode may be useful for
    indoor applications or for operators with
    spectrum. In the TDD mode, the physical channels
    are characterized by the time slots. The uplink
    and downlink transmissions are carried over the
    same radio frequency but in separate time
  • How the data is transmitted?
  • The transmission of data can
    be done in two ways
  • Circuit switching
  • 2) Packet switching

  • Circuit Switching
  • Circuit switching is a
    traditional method and is used for voice traffic.
    In a circuit switched network, a dedicated
    communication path is established between two
    stations through the nodes of the network. The
    path consists of physical links between the nodes
    in the network, and on each of these links a
    logical channel is dedicated to the connection.
    The data is sent over the path as fast as
    possible, and in each node the data is routed to
    the correct outgoing channel without delay. The
    most familiar example of a circuit switched
    network is the Public Switched Telephone Network
  • Packet Switching
  • In a packet switched
    network it is not necessary to dedicate a certain
    capacity for each transmission. Instead, the data
    is sent onto the network in small chunks, called
    packets. Each packet is sent from node to node
    along the path leading from source to
    destination. In every node the packet is examined
    and forwarded onto the right output link. For the
    nodes to be able to recognize the packet and know
    where to forward it, some extra information is
    attached to the packet. This information is
    called a header and contains information about
    for example the sender, the receiver and the
    priority of the packet.

  • W-CDMA uses a data stream of 1024Mbps and is
    passed through an encoder and interleaver. The
    interleaver provides error-protection by shifting
    bit positions so that the effects of interference
    bursts are distributed throughout the data stream
    and can be corrected once the signal is
    deinterleaved at the receiver. The resultant data
    stream is now multiplied by the chip sequence
    (12.288Mbps). This processing is equivalent to
    performing an X-OR operation between the data and
    the spreading code (also known as chipping). A
    band pass filter limits the

  • signal bandwidth to that of the chip rate. The
    original bandwidth of 1024MHz is spread to
    12,288MHz and the processing gain is 12.
  • The signal is now passed through the power
    amplifier (PA) to the antenna. As the signal
    travels through the ether to the receiving
    antenna, it is subjected to interference and
    noise. It also mixes with transmission from other
    mobiles using the same frequency. The resulting
    noise-like signal is picked up by the receiver
    antenna, amplified by the input amplifier (LNA)
    and filtered through the chip rate bandwidth
    filter. The signal is now passed to the
    correlator this will mix the signal with the
    locally generated chip sequence that must be
    synchronized with the transmitter chip sequence.
    At the output of the correlator the actual
    transmitted data stream is reconstituted. Now
    after the de-interleaving and decoding the DATA
    OUT signal will correspond to the original DATA
    IN signal at the input.

  • Making and Receiving a call through W-CDMA
  • Making a call-
  • The mobile user dials the desired digits, and
    presses SEND.
  • Mobile transmits an Origination Message on the
    access channel.
  • The system acknowledges receiving the origination
    by sending a base station acknowledgement on the
    paging channel.
  • The system arranges the resources for the call
    and starts transmitting on the traffic channel.

  • The system notifies the mobile in a Channel
    Assignment Message on the paging channel.
  • The mobile arrives on the traffic channel.
  • The mobile and the base station notice each
    others traffic channel signals and confirm their
    presence by exchanging acknowledgment messages.
  • The base station and the mobile negotiate what
    type of call this will be -- I.e., 13k voice,
  • The audio circuit is completed and the mobile
    caller hears ringing.
  • Receiving a call-
  • All idle mobiles monitor the paging channel to
    receive incoming calls.
  • When an incoming call appears, the paging channel
    notifies the mobile in a General Page Message.
  • A mobile which has been paged sends a Page
    Response Message on the access channel.
  • The system sets up a traffic channel for the
    call, then notifies the mobile to use it with a
    Channel Assignment Message.
  • The mobile and the base station notice each
    others traffic channel signals and confirm their
    presence by exchanging acknowledgment messages.
  • The base station and the mobile negotiate what
    type of call this will be -- I.e., 13k voice,
  • The mobile is told to ring and given a calling
    line ID to display.
  • When the human user presses the send button, the
    audio path is completed and the call proceeds.
  • Applications

  • Applications
  • W-CDMA is currently
    undergoing global standardization for use as the
    next-generation wireless mobile telephone system.
    W-CDMA provides voice services whose voice
    quality is as high as that of a fixed network.
    Also, it provides multimedia mobile communication
    services and global roaming services that enable
    common worldwide use of mobile terminals
    (wireless mobile telephones) as well as the
    conventional voice-call services. The
    standardization organizations in Japan, Europe,
    USA, and other countries have jointly organized a
    framework called the 3rd Generation Partnership
    Project (3GPP).
  • Internet access is
    achieved over a packet switched network whilst
    voice traffic or video conferencing is
    traditionally over circuit switched networks.
    W-CDMA supports both packet and switched
    networking. This support will allow someone to
    access web pages from the Internet, hold a
    videoconference, and download large amounts of
    data/files from a corporate Intranet -all at the
    same time.
  • Here are just a few examples of expected mobile
    multimedia services
  • Entertainment (CD quality audio, video,
    graphics/pictures, games)
  • Information Provisioning

  • Intranet
  • Interactive E-mail, e.g., video postcards (text,
    graphics, video)
  • Videoconferencing
  • Fax
  • Video streaming
  • Electronic Commerce
  • Remote Monitoring
  • Telemedicine

  • Telemetry
  • Office Extension
  • Positioning
  • Fleet Management
  • Database Access
  • Supply Chain Integration
  • Financial Services
  • Shopping
  • Mobile Advertisements

  • Benefits
  • There are many reasons,
    W-CDMA is the technology of choice for next
    generation digital wireless communication
    products and services. Some of them are compiled
  • Outstanding Voice and Call Quality
  • Greatest Coverage for Lower Cost
  • Packet Data
  • Longer Talk Time, Longer Battery Life and
    Smaller Phones
  • Fewer Dropped Calls

  • Improved Security and Privacy
  • Greater Capacity
  • Reduced Background Noise and Interference
  • Spectrum efficiency

  • Conclusion
  • As we have seen, the
    W-CDMA system can provide a high speed radio
    transmission path that is 10 to 100 times faster
    than the conventional 2G cellular phone systems
    (PDC, GSM, and D-AMPS) which will be the key to
    the wide spread use of the 3G mobile
    communication system. The other key feature which
    makes W-CDMA stand out from other mobile
    technologies is increased privacy. W-CDMA phone
    calls will be secure from the casual eavesdropper
    since, unlike an analog conversation, a simple
    radio receiver will not be able to pick
    individual digital conversations out of the
    overall RF radiation in a frequency band.

  • Thus, W-CDMA system has been developed to meet
    mobile communication demands in a true wireless
    environment. The system enables advanced Mobile
    Internet services for the end user. This system
    can make those applications a truth which are
    inconceivable with todays tools enhancing the
    imaginative power of human mind. That, together
    with operator benefits of increased network
    capacity, is what makes W-CDMA systems a sound
  • The development of the
    mobile phone was the starting point for a new
    generation of wireless communication, and the
    development of the W-CDMA marks the beginning of
    another era of mobile communication. Life in this
    new era will be different from anything weve
    ever experienced. Where people will be able to
    reach further..to get information faster and
    easier..to enjoy leisure time more fully..to
    see, know and do more..than ever before. In
    short, we can say that with the advent of W-CDMA
    the world will become smaller than ever and
    quicker than ever.
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