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How other SRW affect your WLAN Performance Abdullah A. Al-Asmari Saudi Aramco/ IT Copyright © Saudi Aramco 2005
Copyright © Saudi Aramco Agenda Wireless Landscape Short Range Wireless WLAN & Bluetooth WLAN & Bluetooth coexistence Solving WLAN & Bluetooth coexistence Conclusion
Copyright © Saudi Aramco Wireless Landscape Data Rate (Mbps) Range ZigBee UWB WPAN 10M WLAN 30M WMAN (Fixed) Cellular (Mobile) WiFi IEEE G Bluetooth 3G Source: WiMedia RFID
Copyright © Saudi Aramco SRW Short Range Wireless refers to a group of technologies that enable wireless data communication across distances of between one and a few hundred meters WLAN, Bluetooth, UWB, ZigBee, and RFID
Copyright © Saudi Aramco WLAN b Standard for 2.4GHz ISM band (80 MHz) Direct Sequence Spread Spectrum (DSSS) 11 Mbps, 500 ft range a Standard for 5GHz U-NII band (300 MHz) OFDM 54 Mbps g Standard in 2.4 GHz OFDM up to 54 Mbps
Copyright © Saudi Aramco Bluetooth Cable replacement RF technology (low cost) Short range (10m, to 100m) 2.4 GHz band (crowded) One Data (700 Kbps) and three voice channels Widely supported by telecommunications PC and consumer electronics companies Few applications beyond cable replacement 2400 MHz MHz 1 MHz 79 hopping channels in 83.5 MHz
Copyright © Saudi Aramco UWB UWB a broad technology solution for creating high-speed, low-cost and low-power WPANs Excellent ranging capability Very high data rates possible 500 Mbps at ~10 feet under current regulations 7.5 Ghz of free spectrum in the U.S. FCC legalized UWB for commercial use Spectrum allocation overlays existing users, but its allowed power level is very low to minimize interference
Copyright © Saudi Aramco ZigBee Promoted by the ZigBee Alliance Very low power, low rate, and short distance transmission standard for wireless sensors network Operates in 868/918 MHz, and 2.4GHz bands using IEEE Low power means low cost and very long (up to years!) battery life making place and forget device applications feasible BAND COVERAGE DATA RATE # OF CHANNEL(S) 2.4 GHz ISM Worldwide 250 kbps MHz Europe 20 kbps MHz ISM Americas 40 kbps 10
Copyright © Saudi Aramco RFID RADIO FREQUENCY IDENTIFICATION uses a semiconductor (micro-chip) in a tag or label to transmit stored data when the tag or label is exposed to radio waves of the correct frequency Very short range (10 meters) sensor technology used to supplement bar-code reader type applications
Copyright © Saudi Aramco Wireless Bands Frequency (GHz) 128k 13.56M M915M RFID ZigBee Bluetooth b/g a UWB U-NII Band ISM Band 2.4G
Copyright © Saudi Aramco Frequency interference 3 2 1
Copyright © Saudi Aramco Frequency interference 2400 MHz MHz Wi-Fi channel (802.11b/g) 1600 hops/s Bluetooth channel RFID ZigBee
Copyright © Saudi Aramco WLAN & Bluetooth Two of the most popular wireless standards – IEEE b/g wireless LAN (WLAN) and Bluetooth – absolutely must play together because they are increasingly co-located in the same handheld device BLUETOOTH AND WLAN ARE ON A COLLISION COURSENOT IN THE MARKET, BUT IN THE AIRWAVES
Copyright © Saudi Aramco WLAN & Bluetooth Marriage of these two popular technologies is quickly becoming a problem because of four interrelated facts: IEEE b/g & Bluetooth use the same 2.4 GHz ISM frequency band (although they use different access mechanisms) Standards bodies did not fully anticipate the range of scenarios in which WLAN and Bluetooth would compete for the same spectrum. As a result, they did not include comprehensive, robust, and cooperative mechanisms in their respective standards to mitigate interference Intense bandwidth utilization when Bluetooth and WLAN transceivers are simultaneously in use can easily overwhelm the error correction mechanisms implemented in the two standards to manage typical interference scenarios Co-location (the presence of Bluetooth and WLAN in the same handheld device) adds the problem of desensitized receivers to the basic spectrum access issues
Copyright © Saudi Aramco WLAN g vs a Pros of a - fastest maximum speed; supports more simultaneous users; regulated frequencies prevent signal interference from other devices Cons of a - highest cost; shorter range signal that is more easily obstructed Pros of g - fastest maximum speed; supports more simultaneous users; signal range is best and is not easily obstructed Cons of g - appliances may interfere on the unregulated signal frequency
Copyright © Saudi Aramco WLAN g vs a The 2.4 GHz band and the power outputs specified for b/802.11g have more worldwide acceptability, which may make these networks a better choice for global deployments Current state of PDAs cannot make use of the a station adapters due to bus limitations on the PDAs g is the most promising option to consider (2.4GHz)
Copyright © Saudi Aramco WLAN b/g It employs three specific, non-overlapping, 22-MHz wide channels.
Copyright © Saudi Aramco Bluetooth Bluetooth wireless technology provides cable-free connections to a wide range of computing and telecommunication devices, including notebook computers, mobile phones and personal digital assistants (PDAs) Bluetooth can support up to three synchronous voice channels, one asynchronous data channel or a channel that simultaneously carries asynchronous data and synchronous voice
Copyright © Saudi Aramco Bluetooth The Bluetooth radio chip separates the 2.4GHz frequency band into 79 hops, 1MHz apart, starting with and ending with Randomly hop at a rate up to 1,600 hops per second The gross data rate of Bluetooth is 1Mbps 2400 MHz MHz Wi-Fi channel (802.11b) 1600 hops/s Bluetooth channel 30 dBm -80 dBm
Copyright © Saudi Aramco Bluetooth When a Bluetooth-enabled device is turned on, it sends omni- directional radio signals asking for a response from any units with an address in a particular range A Piconet is formed if another device within the range responds Any unit within a Piconet can establish a connection with another Piconet to form a Scatternet When a Piconet is established, the initiating unit acts as a master and the others act as slaves for the duration of the connection A Piconet consists of one master and up to seven slave units
Copyright © Saudi Aramco Bluetooth The Bluetooth Special Interest Group (SIG) commissioned Millward Brown Group to conduct a study on consumer awareness, attitude and usage of Bluetooth wireless technology compared with other wireless technologies. The study polled 1,300 consumers from ages 18 to 70 in the US, UK and Japan during the autumn of 2003 and again in the autumn of 2004 It is encouraging to see how consumer awareness mirrors the rise in volumes of Bluetooth products over the last year Select which technology allows mobile devices to connect wirelessly? BluetoothUSAUKJapan
Copyright © Saudi Aramco Bluetooth Source: In-Stat/Philips
Copyright © Saudi Aramco WLAN & Bluetooth Coexistence Interference occurs when a Bluetooth and a WLAN device are in close proximity and simultaneously transmit and receive wireless signals
Copyright © Saudi Aramco WLAN & Bluetooth Coexistence The two technologies use different methods for signal transmission: carrier sense multiple access (CSMA) and frequency hopping spread spectrum CSMA is used by an b/g transceiver to listen for a clear channel before transmitting a signal that is approximately 20MHz wide and typically occupies one to three possible non-overlapping channels spaced 25MHz apart A simple calculation demonstrates that a Bluetooth transmitter will output a signal that collides with an b/g signal about 25 percent of the time
Copyright © Saudi Aramco WLAN & Bluetooth Coexistence Distance between Wi-Fi and Bluetooth tends to prevent them from interfering, but in a PDA this is not possible. When Bluetooth and Wi-Fi are put into the same device, the transmitted signals from one network appear on the receiver of the other making them interfere with the each other (Collocation Interference) If the traffic in the cell is light enough, the problem can be corrected within the existing standards. Both standards define error correction protocols that basically require the system to fall back and retransmit the data If, however, traffic in the cell is heavy, retransmission only makes matters worse by creating even more traffic. Valid data throughput can drop dramatically
Copyright © Saudi Aramco Performance with WLAN & Bluetooth Coexistence In the case of WiFi, a separation of 10 m results in minimal impact for short-range WiFi use, with increasing impact over longer ranges A separation of only 2 cm, has a much more profound impact. In that situation, Bluetooth can shut down WiFi for all but short-range use
Copyright © Saudi Aramco Performance with WLAN & Bluetooth Coexistence In the case of Bluetooth, the effect is different. Wi-Fi has minimal impact on Bluetooth when separated by 10 m, regardless of range A 2 cm separation, drastically reduces Bluetooth throughput even for short ranges and quickly shuts it down with increasing range
Copyright © Saudi Aramco Solving WLAN & Bluetooth Coexistence The IEEE recommended practices. The mechanisms fall into two categories: collaborative and non-collaborative Non-collaborative mechanisms require that Bluetooth or WLAN take independent means to avoid interference: Adaptive Frequency Hopping (AFH) Adaptive Packet Selection And Scheduling (APSS) Collaborative mechanisms require that Bluetooth and WLAN exchange information when accessing the medium: Packet Traffic Arbitration (PTA) Alternating Wireless Medium Access (AWMA) Deterministic Spectral Excision (DSE)
Copyright © Saudi Aramco Adaptive Frequency Hopping (AFH) Bluetooth 1.2 specification includes Adaptive Frequency Hopping (AFH) to help Bluetooth devices find and avoid interference Using AFH, a channel can be classified as good or bad, so that bad channels are avoided and replaced in the hopping sequence by pseudo-randomly selecting out of the remaining good channels Once a Bluetooth device determines that a WLAN device is operating within the 2.4 GHz band, the frequency hopping channels that overlap are designated as bad and avoided
Copyright © Saudi Aramco Adaptive Frequency Hopping (AFH) Bluetooth 1.2 can reduce its hopping sequence from 79 1MHz bands to as few as 15 The throughput of the Bluetooth link using AFH is at 100% at a distance of 2 m. When their distance is closer than 0.5 m, the Bluetooth throughput - even using AFH – decreases AFH as a standalone technique is insufficient when Bluetooth and devices are co-located in the same design
Copyright © Saudi Aramco Adaptive Packet Selection And Scheduling (APSS) Bluetooth provides a wide range of packet types to select from, with various payload lengths and forward error correction (FEC) options Using shorter packets, for instance, reduces the amount of data needed to be present when interference occurs and can actually improve throughput compared to larger packets Dropping the use of FEC when a Wi-Fi system is the cause of interference can also help Developers can implement the APSS technique predominantly in the MAC layer, while keeping the hardware structure virtually unchanged APSS is an inappropriate technique for Bluetooth voice applications
Copyright © Saudi Aramco Packet Traffic Arbitration (PTA) The PTA technique uses a control entity that receives per- transmission transmit requests from each network stack and issues transmission-confirmation signals to the stacks to indicate whether the transmission can proceed Does not require that either network device be a master device The PTA controller can simply deny any requests that would result in a collision Requires a number of status signals from the two wireless devices The controller needs to know the traffic priority of each packet It needs to know the Bluetooth frequency in use to determine whether a collision is likely Requires at least two additional wires to communicate Designers can implement the approach only when the hardware designs of the two wireless chips are compatible
Copyright © Saudi Aramco Alternating Wireless Medium Access (AWMA) AWMA is a simple procedure that divides the time interval for transmission and reception into a Bluetooth interval and an interval For this technique to work, the WLAN and Bluetooth devices must be connected, implying that they are collocated in the same physical unit In addition, all nodes in the WLAN must connect to the same access point so that they are synchronized The Bluetooth device must be in its master mode The slave device can transmit only if it receives permission from the master This mechanism has the substantial disadvantage of requiring in- field upgrades to all access points already in use
Copyright © Saudi Aramco Deterministic Spectral Excision (DSE) DSE starts from the perspective that Bluetooth be considered a narrowband interferer for the 22 MHz wide b/g signal It puts a null in the b/gs receiver at the frequency of the Bluetooth signal the b/g receiver needs to know the frequency hopping pattern as well as the timing of the Bluetooth transmitter This additional signal processing adds significant complexity to existing WLAN receivers and does not solve the collocation issue
Copyright © Saudi Aramco Other Practices AIM (adaptive-interference management); control the direction of the antennas in use Inter-Digital, an RF-component company, has developed AIM (adaptive- interference management) technology that can enable Wi-Fi networks to adapt their operating frequencies in response to interference The company also offers an AIM antenna that uses beam forming to create a directional antenna that has a strong null in one direction which allows the system to switch among omni-directional and two opposite- pointing directional antennas to find the pattern that minimizes interference
Copyright © Saudi Aramco TI coexistence solution TI has developed a coexistence solution for simultaneous functionality of b/g and Bluetooth in small form factors, including cell phones, laptop computers, PDAs, web tablets and other types of mobile terminals It provides intelligent and seamless coordination between TIs WLAN and Bluetooth technologies at MAC layer No RF isolation is needed between the and Bluetooth antennas Takes advantage of the general purpose coexistence interface BUS connection between TIs MAC processors and TIs advanced Bluetooth system on-a-chip
Copyright © Saudi Aramco TI coexistence solution Software monitors WLAN and Bluetooth traffic patterns and, when both and Bluetooth require bandwidth, it uses multiplexing techniques to allocate the bandwidth for simultaneous functions At any time, all of the available bandwidth can be dedicated to either or Bluetooth, as long as one or the other is idle The coexistence solution can intelligently set different priorities depending on the time-sensitive nature of the communication
Copyright © Saudi Aramco Conclusion 2.4GHz is a crowded band All wireless technologies that reside in 2.4GHz can co-exist without interference except with Bluetooth presence RFID and ZigBee occupying very narrow bandwidth which allow them to co-exist with b/g without interference Since Bluetooth using Frequency Hopping scheme, it will interfere with any occupying wireless at 2.4GHz band Bluetooth and Wi-Fi must coexist The techniques that designers can apply depend on the chip sets in use, but the greatest flexibility comes from devices that can coordinate their activities
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