Wifi: g Protocol By Truc Truong CS158B Prof. Mark Stamp

Introduction  The wireless market has been enjoying a steady growth.  Not connected to wires, people are able to access data and information anywhere they go.  The increase in mobility has changed the way of networking.  Also, open up new markets for the technology industry.

How companies benefits from wireless?  Doctors and Nurses traditionally access patients records from charts next to the patient’s bed. Imagine if patients’ charts are now accessible from a palm-pilot or tablet PC. With wireless access to network data, hospitals now are beginning to change their network architecture.

How companies benefits from wireless? Cont.  Imagine a business meeting taking place in 10mins for 20 people that need access to network resources. Not so easy laying out the wiring needed, if the room isn’t pre-wired for such an event. Not to mention, network troubleshooting if there’s problems with connectivity. With wireless, a network administrator simply put up an Access Point (AP) configure it and everyone at the meeting will be able to gain access.

History of Wireless  Network has always been predominately wired networks (ethernet 802.3). The diversity created a cheap and competitive market for vendors.  These companies strived very hard to provide consumers with latest networking technology; this included wireless technology.  Early wireless network operated around 900Mhz band and had a bandwidth of 1-2Mbps. These early products where expensive.  Wireless became popular in retail, warehouse companies, and home users.

History of Wireless  In 1991, companies like Aironet and other wireless companies pushed for standards to wireless technologies.  Around 1992, companies began producing 2.4Ghz (unlicensed) frequence band wireless products. This created cheaper wireless products for consumers.  In 1997, IEEE released the standards for wireless.

Wireless Market

The Protocol – Physical Layer  protocol places parameters on both the physical (PHY) and access control (MAC) layers of the network. The physical layer handles the transmission of data between all nodes by using either direct sequence spread spectrum (DSSS), frequency-hopping spread spectrum (FHSS), or infrared (IR).

The Protocol – Operation range  protocol operates in the 2.4Ghz – 5Ghz frequency band, which are unlicensed for industrial, scientific and medical field.  Infrared Red protocol operates in the ,000 Ghz range.  IR provides better security to eavesdropping, but is a line-of-sight service. While, 2Ghz and 5Ghz uses radio wave which can penetrate solid objects such as: trees, and buildings.

The Protocol – Protocol Output

The Protocol – Mac layer  The access control (MAC) layer is responsible for maintaining order in the use of a shared medium. The MAC layer uses CSMA/CA protocol to specify a carrier for sense multiple access with collision avoidance.  CSMA/CA protocol works when a node receives a packet for transmission, it listens to the network to check no other nodes are transmitting. If the network is clear, it then transmits the packets. If the network is busy, the protocol then chooses a random “backoff factor” which is the amount of time the node must wait until it can transmit the packets. During the time the network is clear the node decrements the “backoff counter”. If the network is busy it does not decrement the “backoff counter”. Once the “backoff counter” reaches zero the node then transmit the packets. The probability that two nodes will choose the same “backoff counter” is very small, so the collisions between packets are rare.  The reason that IEEE had to create a new protocol (CSMA/CA) to listen to the network, because the transmitting wireless nodes can’t hear other nodes on the network when it’s transmitting, since its signal will drown out any other arriving at the node.

The Protocol – sending data  When a packet is ready for transmission, the node sends out a short ready-to-send (RTS) packet containing information on the length of the transmitting packet.  The receiving node gets the RTS, then responds with a short clear-to-send (CTS) packet. After the connection has been established the two nodes then begin the communication.  Once the transmission is finished successfully the transmitting node then send a cyclic redundancy check (CRC), and the receiving node transmits an acknowledgement (ACK) packet.

The g Protocol  In July 1999, IEEE pushed for another protocol of to extend the 2.4Ghz frequency to increase data rate beyond 20Mbps.  g was approved in June 2003 and was backward compatible with b

The comparison

The g Protocol  To achieve the desired data rate, g uses Orthogonal Frequency Division Multiplexing (OFDM) and Complementary Code Keying (CCK) modulation.  However, g was conceived by using physic of wave form properties.  There is an inverse relationship between wavelength and range. A signal transmitted at a lower frequency range of spectrum will carry further than a signal transmitted in a higher frequency range.  b operating at 5Ghz provide high data rate, but had low range.  So, it is important that g should operate in 2.4Ghz frequency band.

The g Protocol  The new protocol focused on transmit power and receiver sensitivity.  High power coming from the radio’s transmitter leads to desensitization, a phenomenon known as Error Vector Magnitude (EVM). This phenomenon leads to a counterproductive stage, whereby increasing transmit power means the range of the device decreases.  g achieved the b data rates by using lower transmit power under OFDM standard. By the performance of g one can see that it is a superset of b. So, it’s vital that g devices be able to operate with g devices. In order, to do this each client performs a procedure to select the best transmission rate.

Data Rate and Range

Conclusion  g is an exciting technology that offers the performance of a, and the range of b.  It also provides investment solution to companies already using b AP devices, whose looking to upgrade to g devices in the future.  g technology will be the standard for next generation of wireless networking.  The benefits of g are so great that is compelling to for customers to upgrade. Some of these benefits are: providing an increase in LAN speed, backward compatible with b products, and offer higher range and coverage for networks.

Reference  Broadcom, The New Mainstream Wireless LAN standard, Irvine, CA,  Cisco Systems, Capacity, Coverage, and Deployment Considerations, San Jose, CA,  Lough, Daniel L. and et al, A Short Tutorial on Wireless LANs and IEEE , Virginia Polytechnic, Blacksburg, Virginia,  services.ufl.edu/provided_services/wireless/back ground.html