Wireless Networks and Protocols. Ram Dantu This material is compiled from various sources including several industrial presentations, university lecture notes etc.,. Why Wireless? Reduced cost More flexibility for locating equipment (deployment ease) User mobility
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
This material is compiled from various sources including several industrial presentations, university lecture notes etc.,
Limitations of Wireless
Signal paths between a transmitter and a receiver can contain
The presence of these multiple paths and/or physical obstructions implies
Furthermore, fading can vary in time, frequency, and space (for
example, as users move).
In addition to fading, wireless transmissions are susceptible to
interference from other users and/or systems.
Consequently, the wireless media can significantly impact the
transmission and reception of signals (much more so than
transmissions on wired networks).
Thus, network protocols designed assuming wired channel
characteristics may not perform well in wireless scenarios.
Considerations in Design and Study
Centralized wireless networks have two types of transceivers:
access points (AP's) and user terminals.
AP's have wired connections to other AP's and/or larger wired
This implies control is centralized at the AP's, i.e., user terminals
communicate only to AP's -> a spoke-and-wheel network configuration
Non-centralized networks can also contain both AP's and user terminals
but communication is not limited between AP and user terminals only.
Ad hoc, peer-to-peer connections are possible, as is dynamic routing of
information from source to destination.
Services or Features: Voice and data through handheld phones.
Coverage Area: Continuous coverage. At times limited to
Limitations: Available bandwidth is very low for most data
Examples: AMPS, IS-136, IS-95, GSM, WCDMA, cdma2000, etc.
Services or Features: Traditional LAN extended with wireless
Coverage Area: Used only in local environments
Limitations: Limited range.
Examples: IEEE 802.11 suite (a,b,g)
Services or Features: Helps to determine the three-dimensional
position, velocity, and time.
Coverage Area: Anyplace on earth.
Examples: GNSS, NAVSTAR, GLONASS
Services or Features: Voice paging and messaging.
Coverage Area: Almost anyplace on earth.
Examples: Iridium, Teledesic.
Services or Features: To connect different PC's in the house to
share files and devices such as printers. Also to connect different
appliances in the house.
Coverage Area: Anywhere in the house.
Limitations: Limited to a home.
This can also be categorized as a local area network.
Services or Features: Group of users share data with each other
for a short period of time.
Coverage Area: Equal to that of a LAN, but without fixed
Limitations: Limited range.
Examples: Bluetooth, defense applications. Battlefields, disaster
Services or Features: A large number of tiny (cheap, low-power)
sensors with wireless capabilities. Collected data is transmitted
back to a central processor.
Coverage Area: Relatively small terrain.
Limitations: Very limited range, scalability problems (under certain
Examples: Defense and civilian applications. Monitor inhospitable
or inaccessible terrain.
PacketNetworkA Simple Wireless Network
Mobile Switching Center (MSC)
Mobile Data Set
Base Station Controller (BSC)
Packet Inter-Working Function
Base Transceiver System (BTS)
Challenge is to keep connection and not loose any data during handoff operation
Handoff: A handoff mechanism is needed to maintain connectivity as devices move, while minimizing disruptions to ongoing calls. This mechanism should exhibit low latency, incur little or no data loss, and scale to a large network.”
Handoffs == ( Hard || Soft )
Typical US city BTS Map
2G/3G RAN Network (Traditional)
Interoffice distance (costs per mile) cost + Fixed Cost
2SDU and soft handoff
Terminal scans control channels and locks on to strongest one.
If can’t find a strong enough signal, “no service”
With receiver turned to strongest control channel, terminal
extracts important information from broadcast channel.
On interpreting this broadcast information, terminal turns on “roaming” sign, determines DCC, paging channels, etc.
Once this initialization is complete, mobile enters idle mode.
When no call in progress, terminal monitors paging messages in order to detect arrival of a new call.
(one of broadcast
Page for User with MIN X
User with Mobile Identification Number (MIN) X
Power consumed by radio receiver while it waits for paging on “roaming” sign, determines DCC, paging channels, etc.
message has strong influence on standby time of terminal’s
Terminals can operate in sleep mode when no call in progress.
In this mode, terminal turns off its receiver for significant fraction
of time. Wakes up for short period of time.
If there is paging message for terminal, BS schedules message to
arrive during brief wake-up interval. This is synchronized by using
a hyperframe counter.
Paging messages arrive in SPACH blocks of superframe. Indicates
assigned traffic channels, etc.
HLR on “roaming” sign, determines DCC, paging channels, etc. contains subscription information of a set of terminals and also records terminal’s current location and status. Information about each terminal is accessed using mobile identification number.
A call request for a terminal arrives at terminal’s home MSC.
Home MSC interrogates HLR in order to determine location of terminal. MSC then coordinates actions to page terminal in visited system.
VLR stores information about terminals currently in service area.
This information is used to setup calls initiated by cellular users
And to deliver calls directed to cellular users. Service area of VLR
Spans coverage areas of one or more MSC’s.
Mobile Assisted Handoff (MAHO)
A terminal tuned to a digital traffic channel relies on MAHO to move
Its call to a new BS.
With MAHO terminal with call in progress monitors quality of
Signal on active traffic channel.
During intervals in each frame when it is not required to transmit/
Receive information on active traffic channel, terminal measures
Strength of signals received from surrounding BS.
Terminal reports measurements to its own BS on SACC.
Order” and “stop measurement order” messages to terminals
With calls in progress.
“Measurement order” messages identify active channels in
Surrounding cells. Terminal tunes to these channels and
Observes signal strengths.
Terminal measures bit error rate (BER) and received signal
Strength indication (RSSI).
MAHO monitors quality of signal received at terminal as well as
At BS. Can react promptly to signal-quality problems.
When signal at another BS exceeds current for some period
Of time, MSC coordinates between two BS to switch user to
New BS. Switch requires terminal to tune into new channel.
CDMAo r “Spread Spectrum”
cluster size (N = 3)
(N = 4)
(N = 5)
N = 7