WIDEBAND CODE DIVISION MULTIPLE ACCESS

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INTRODUCTION

• WIDEBAND CODE DIVISION MULTIPLE ACCESS
• 3G TECHNOLOGY FOR MOBILE COMMUNICATION

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• ABSTRACT
• 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.

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• 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
  speed.
• 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.

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• WHY 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
  multimedia.
• BCABACCAB
• 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.

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• 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.

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• ARCHITECTURE OF THE RADIO-INTERFACE
• 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.

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• 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
  entities
• 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

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• 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
  information.
• 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.

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• 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.

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• 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.

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• 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.

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• 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
  guaranteed.

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• 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
  guaranteed.
• 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
  measurements.

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• 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
  data.

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• 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.

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• MODES OF TRANSMISSION
• Two duplex modes of transmission have been
  standardized
• Time Division Duplex (TDD).

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• 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
  intervals.
• How the data is transmitted?
• The transmission of data can
  be done in two ways
• Circuit switching
• 2) Packet switching

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• 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
  (PSTN).
• 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.

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• A WCDMA COMMUNICATION SYSTEM
• 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

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• 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.

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• 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.

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• 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,
  etc.
• 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,
  etc.
• 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

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• 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

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

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

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• 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
  below
• Outstanding Voice and Call Quality
• Greatest Coverage for Lower Cost
• Packet Data
• Longer Talk Time, Longer Battery Life and
  Smaller Phones
• Fewer Dropped Calls

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

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• 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.

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• 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
  investment.
• 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.