With the rapid development of wireless communication networks, it is expected that fourth generation (4G) mobile systems will be launched within a decade. 4G mobile systems focus on seamless integration of existing wireless technologies including wireless wide area network (WWAN), wireless local area network (WLAN), and Bluetooth. This is in contrast with third generation (3G) mobile systems, which merely focuses on developing new standards and hardware. The recent convergence of the Internet and mobile radio has accelerated the demand for “ Internet in the pocket, ” as well as for radio technologies that increase data throughput and reduce the cost per bit. Mobile networks are going multimedia, potentially leading to an explosion in throughput from a few bytes for the short message service (SMS) to a few kilobits per second (kbps) for the multimedia messaging service (MMS) to several 100 kbps for video content. In addition to wide-area cellular systems, diverse wireless transmission technologies are being deployed, including digital audio broadcast (DAB) and digital video broadcast (DVB) for wide-area broadcasting, local multipoint distribution service (LMDS), and multichannel multipoint distribution service (MMDS) for fi xed wireless access. IEEE 802.11b, 11a, 11g, 11n, and 11h standards for WLANs are extending from the enterprise world into public and residential domains. Because they complement cellular networks, these new wireless network technologies and their derivatives may well prove to be the infrastructure components of the future 4G mobile networks when multistandard terminals become widely available. This is already the case for Wi-Fi in the public “ hotspots, ” which is being deployed by mobile operators around the world with the aim to offer seamless mobility with WWANs.
The 4G systems will encompass all systems from various networks, public to private, operator-driven broadband networks to personal areas, and ad hoc networks. The 4G systems will be interoperable with second-generation (2G) and 3G systems, as well as with digital (broadband) broadcasting systems. The 4G intends to integrate from satellite broadband to high altitude platform to cellular 2G and 3G systems to wireless local loop (WLL) and broadband wireless access (BWA) to WLAN, and wireless personal area networks (WPANs), all with IP as the integrating mechanism.
Source of Information : Elsevier Wireless Networking Complete
Wednesday, August 29, 2012
Sunday, August 26, 2012
Spectrum Allocation for WiMAX
The IEEE 802.16 specifi cation applies across a wide swath of RF spectrum. There is no uniform global licensed spectrum for WiMAX in the United States. The biggest segment available is around 2.5 GHz and is already assigned — primarily to Sprint Nextel. Elsewhere in the world, the most likely bands used will be around 3.5 GHz, 2.3/2.5 GHz, or 5 GHz, with 2.3/2.5 GHz probably being most important in Asia.
There is some prospect that some of a 700 MHz band might be made available for WiMAX in the United States, but it is currently assigned to analog TV and awaits the complete rollout of HD digital TV before it can become available, likely by 2009. There are several variants of 802.16, depending on local regulatory conditions and thus of which spectrum is used.
Mobile WiMAX based on the 802.16e standard will most likely be in 2.3 and 2.5 GHz frequencies — low enough to accommodate the NLOS conditions between the base station and mobile devices. The key technologies in 802.16e on PHY levels are OFDMA and SOFDMA. OFDMA uses a multicarrier modulation in which the carriers are divided among users to form subchannels. For each subchannel, the coding and modulation are adapted separately, allowing channel optimization on a smaller scale (rather than using the same parameters for the whole channel). This technique optimizes the use of spectrum resources and enhances indoor coverage by assigning a robust scheme to vulnerable links. SOFDMA is an enhancement of OFDMA that scales the number of subcarriers in a channel with possible values of 128, 512, 1024, and 2048.
802 .16e includes power-saving and sleep modes to extend the battery life of mobile devices. 802.16e also supports hard and soft handoffs to provide users with seamless connections as they move across coverage areas of adjacent cells. Other improvements for mobile devices include a real-time polling service to provide QoS, HARQ scheme to retransmit erroneous packets, and private key-management schemes to help with the distribution of encryption keys.
Source of Information : Elsevier Wireless Networking Complete
There is some prospect that some of a 700 MHz band might be made available for WiMAX in the United States, but it is currently assigned to analog TV and awaits the complete rollout of HD digital TV before it can become available, likely by 2009. There are several variants of 802.16, depending on local regulatory conditions and thus of which spectrum is used.
Mobile WiMAX based on the 802.16e standard will most likely be in 2.3 and 2.5 GHz frequencies — low enough to accommodate the NLOS conditions between the base station and mobile devices. The key technologies in 802.16e on PHY levels are OFDMA and SOFDMA. OFDMA uses a multicarrier modulation in which the carriers are divided among users to form subchannels. For each subchannel, the coding and modulation are adapted separately, allowing channel optimization on a smaller scale (rather than using the same parameters for the whole channel). This technique optimizes the use of spectrum resources and enhances indoor coverage by assigning a robust scheme to vulnerable links. SOFDMA is an enhancement of OFDMA that scales the number of subcarriers in a channel with possible values of 128, 512, 1024, and 2048.
802 .16e includes power-saving and sleep modes to extend the battery life of mobile devices. 802.16e also supports hard and soft handoffs to provide users with seamless connections as they move across coverage areas of adjacent cells. Other improvements for mobile devices include a real-time polling service to provide QoS, HARQ scheme to retransmit erroneous packets, and private key-management schemes to help with the distribution of encryption keys.
Source of Information : Elsevier Wireless Networking Complete
Wednesday, August 22, 2012
WiMAX Media Access Control (MAC)
The IEEE 802.16 MAC is significantly different from IEEE 802.11b Wi-Fi MAC. In Wi-Fi, the MAC uses contention access — all subscribers wishing to pass data through an AP compete for the AP’s attention on a random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. This makes services, such as VoIP or IPTV which depend on a determined level of QoS, difficult to maintain for large numbers of users.
The MAC layer of 802.16 is designed to serve sparsely distributed stations with high data rates. Subscriber stations are not required to listen to one another because this listening might be difficult to achieve in the WiMAX environment. The 802.16 MAC is a scheduling MAC where the subscriber only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber, meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription. It is also more bandwidth-efficient. The scheduling algorithm allows the BS to control QoS by balancing the assignment among the needs of subscribers.
Duplexing , a station’s concurrent transmission and reception, is possible through TDD and FDD. In TDD, a station transmits then receives (or vice versa) but not at the same time. This option helps reduce subscriber station costs, because the radio is less complex. In FDD, a station transmits and receives simultaneously on different channels.
The 802.16 MAC protocol is connection-oriented and performs link adaptation and ARQ functions to maintain target BER while maximizing the data throughput. It supports different transport technologies such as IPv4, IPv6, Ethernet, and ATM. This lets service providers use WiMAX independently of the transport technology they support.
The recent WiMAX standard, which adds full mesh networking capabilities, enables WiMAX nodes to simultaneously operate in “ subscriber ” and “ base station ” mode. This blurs the initial distinction and allows for widespread adoption of WiMAX-based mesh networks and promises widespread WiMAX adoption. Mobile WiMAX with OFDMA and scheduled MAC allows wireless mesh networks to be much more robust and reliable.
Source of Information : Elsevier Wireless Networking Complete
The MAC layer of 802.16 is designed to serve sparsely distributed stations with high data rates. Subscriber stations are not required to listen to one another because this listening might be difficult to achieve in the WiMAX environment. The 802.16 MAC is a scheduling MAC where the subscriber only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber, meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription. It is also more bandwidth-efficient. The scheduling algorithm allows the BS to control QoS by balancing the assignment among the needs of subscribers.
Duplexing , a station’s concurrent transmission and reception, is possible through TDD and FDD. In TDD, a station transmits then receives (or vice versa) but not at the same time. This option helps reduce subscriber station costs, because the radio is less complex. In FDD, a station transmits and receives simultaneously on different channels.
The 802.16 MAC protocol is connection-oriented and performs link adaptation and ARQ functions to maintain target BER while maximizing the data throughput. It supports different transport technologies such as IPv4, IPv6, Ethernet, and ATM. This lets service providers use WiMAX independently of the transport technology they support.
The recent WiMAX standard, which adds full mesh networking capabilities, enables WiMAX nodes to simultaneously operate in “ subscriber ” and “ base station ” mode. This blurs the initial distinction and allows for widespread adoption of WiMAX-based mesh networks and promises widespread WiMAX adoption. Mobile WiMAX with OFDMA and scheduled MAC allows wireless mesh networks to be much more robust and reliable.
Source of Information : Elsevier Wireless Networking Complete
Friday, August 17, 2012
WiMAX PHY
The 802.16 PHY supports TDD and full and half-duplex frequency-division duplex (FDD) operations; however, the initial release of mobile WiMAX only supports TDD. Other advanced PHY features include adaptive modulation and coding (AMC), hybrid ARQ (HARQ), and fast channel feedback (CQICH) to enhance coverage and capacity of WiMAX in mobile applications.
For the bands in the 10 – 66 GHz range, 802.16 defi nes one air interface called Wireless MAN-SC. The PHY design for the 2 – 11 GHz range (both licensed and unlicensed bands) is more complex because of interference. Hence, the standard supports burst-by-burst adaptability for modulation and coding schemes and specifies three interfaces. The adaptive features at the PHY allow trade-off between robustness and capacity. The three air interfaces for the 2 – 11 GHz range are:
● Wireless MAN — SCa uses single carrier modulation.
● Wireless MAN — OFDM uses a 256-carrier OFDM. This air interface provides multiple access to different stations through TDMA.
● Wireless MAN — OFDM uses a 2048-carrier OFDM scheme. The interface provides multiple access by assigning a subset of the carriers to an individual receiver.
Support for QPSK, 16-QAM, and 64-QAM are mandatory in the downlink with mobile WiMAX. In the uplink 64-QAM is optional. Both convolutional code and turbo code with variable code rate and repetition coding are supported. The combinations of various modulation and code rates provide a fi ne resolution of data rates. The frame duration is 5 ms. Each frame has 48 OFDM symbols with 44 OFDM symbols available for data transmission.
The base station (BS) scheduler determines the appropriate data rate for each burst allocation
based on the buffer size, channel propagation conditions at the receiver, etc. A channel quality indicator (CQI) channel is used to provide channel state information from the user terminals
to the BS scheduler.
WiMAX provides signaling to allow fully asynchronous operation. The asynchronous operation allows variable delay between retransmissions which gives more flexibility to the scheduler at the cost of additional overhead for each retransmission. HARQ combined with CQICH and AMC provides robust link adoption in the mobile environment at vehicular speeds in excess of 120 km/h.
Source of Information : Elsevier Wireless Networking Complete
For the bands in the 10 – 66 GHz range, 802.16 defi nes one air interface called Wireless MAN-SC. The PHY design for the 2 – 11 GHz range (both licensed and unlicensed bands) is more complex because of interference. Hence, the standard supports burst-by-burst adaptability for modulation and coding schemes and specifies three interfaces. The adaptive features at the PHY allow trade-off between robustness and capacity. The three air interfaces for the 2 – 11 GHz range are:
● Wireless MAN — SCa uses single carrier modulation.
● Wireless MAN — OFDM uses a 256-carrier OFDM. This air interface provides multiple access to different stations through TDMA.
● Wireless MAN — OFDM uses a 2048-carrier OFDM scheme. The interface provides multiple access by assigning a subset of the carriers to an individual receiver.
Support for QPSK, 16-QAM, and 64-QAM are mandatory in the downlink with mobile WiMAX. In the uplink 64-QAM is optional. Both convolutional code and turbo code with variable code rate and repetition coding are supported. The combinations of various modulation and code rates provide a fi ne resolution of data rates. The frame duration is 5 ms. Each frame has 48 OFDM symbols with 44 OFDM symbols available for data transmission.
The base station (BS) scheduler determines the appropriate data rate for each burst allocation
based on the buffer size, channel propagation conditions at the receiver, etc. A channel quality indicator (CQI) channel is used to provide channel state information from the user terminals
to the BS scheduler.
WiMAX provides signaling to allow fully asynchronous operation. The asynchronous operation allows variable delay between retransmissions which gives more flexibility to the scheduler at the cost of additional overhead for each retransmission. HARQ combined with CQICH and AMC provides robust link adoption in the mobile environment at vehicular speeds in excess of 120 km/h.
Source of Information : Elsevier Wireless Networking Complete
Tuesday, August 14, 2012
World Interoperability for MicroAccess, Inc. (WiMAX)
WiMAX is an advanced technology solution based on an open standard, designed to meet the need for very high speed wide area Internet access, and to do so in a low-cost, flexible way. It aims to provide business and consumer broadband service on the scale of the metropolitan area network (MAN). WiMAX networks are designed for high-speed data and will spur innovation in services, content, and new mobile devices. WiMAX is optimized for IP-based high-speed wireless broadband which will provide for a better mobile wireless broadband Internet experience.
The WiMAX product certifi cation program ensures interoperability between WiMAX equipment from vendors worldwide. The certifi cation program also considers interoperability with (HIPERMAN), the European telecommunication standards institute’s MAN standard.
With its large range and high transmission rate, WiMAX can serve as a backbone for 802.11 hotspots for connecting to the Internet. Alternatively, users can connect mobile devices such as laptops and handsets directly to WiMAX base stations without using 802.11. Mobile devices connected directly can achieve a range of four to six miles, because mobility makes links vulnerable. The WiMAX technology can also provide fast and cheap broadband access to markets that lack infrastructure (fi ber optics or copper wire), such as rural areas and unwired countries. WiMAX can be used in disaster recovery scenes where the wired networks have broken down. It can be used as backup links for broken wired links.
WiMAX can typically support data rates from 500 kbps to 2 Mbps. WiMAX also has clearly defi ned QoS classes for applications with different requirements such as VoIP, real-time video streaming, file transfer, and web traffic. A cellular architecture similar to that of mobile phone systems can be used with a central base station controlling downlink/uplink traffic.
WiMAX is a family of technologies based on IEEE 802.16 standards. There are two main types of WiMAX today: fi xed WiMAX (IEEE 802.16d — 2004) and mobile WiMAX (IEEE 802.16e — 2005). Fixed WiMAX is a point-to-multipoint technology, whereas mobile WiMAX is a multipoint-to-multipoint technology, similar to that of a cellular infrastructure. Both solutions are engineered to deliver ubiquitous high-throughput broadband wireless service at a low cost. Mobile WiMAX uses orthogonal frequency division multiple access (OFDMA) technology which has inherent advantages in latency, spectral efficiency, advanced antenna performance, and improved multipath performance in an NLOS environment. Scalable OFDMA (SOFDMA) has been introduced in IEEE 802.16e to support scalable channel bandwidths from 1.25 to 20 MHz. Release 1 of mobile WiMAX will cover 5, 7, 8.75, and 10 MHz channel bandwidths for licensed worldwide spectrum allocations in 2.3, 2.5, 3.3, and 3.5 GHz frequency bands. Also, next generation 4G wireless technologies are evolving toward OFDMA and IP-based networks as they are ideal for delivering cost-effective highspeed wireless data services.
The WiMAX specifi cation improves upon many of the limitations of the Wi-Fi standard (802.11b) by providing increased bandwidth and stronger encryption.
The 802.16 standard was designed mainly for point-to-multipoint topologies, in which a base station distributes traffic to many subscriber stations that are mounted on rooftops. The pointto-multipoint confi guration uses a scheduling mechanism that yields high efficiency because stations transmit in their scheduled slots and do not contend with one another. WiMAX does not require stations to listen to one another because they encompass a larger area. This scheduling design suits WiMAX networks because subscriber stations might aggregate traffic from several computers and have steady traffic, unlike terminals in 802.11 hotspots, which usually have bursty traffi c. The 802.16 also supports a mesh mode, where subscriber stations can communicate directly with one another. The mesh mode can help relax the LOS requirement and ease the deployment costs for high-frequency bands by allowing subscriber stations to relay traffi c to one another. In this case, a station that does not have LOS with the
base station can get its traffi c from another station. Mobile WiMAX systems offer scalability in both radio access technology and network architecture, thus providing a great deal of flexibility in network deployment options and service offerings. Some of the salient features supported by WiMAX are:
● High data rates: The inclusion of MIMO antenna techniques along with flexible subchannelization schemes, advanced coding, and modulation all enable the mobile WiMAX technology to support peak downlink data rates of 63 Mbps per sector and peak uplink data rates of up to 28 Mbps per sector in a 10 MHz channel.
● QoS: The fundamental premise of the IEEE 802.16 MAC architecture is QoS. It defines service fl ows which can map to DiffServ code points or MPLS flow labels that enable end-to-end IP-based QoS. Additionally, sub-channelization and MAP-based signaling schemes provide a flexible mechanism for optimal scheduling of space, frequency, and time resources over the air interface on a frame-by-frame basis.
● Scalability: Mobile WiMAX is designed to be able to scale to work in different channelization from 1.25 to 20 MHz to comply with varied worldwide requirements as efforts proceed to achieve spectrum harmonization in the longer term.
● Security: Support for a diverse set of user credentials exists including SIM/USIM cards, smart cards, digital certifi cates, and user name/password schemes based on the relevant extensible authentication protocol (EAP) methods for the credential type.
● Mobility: Mobile WiMAX supports optimized handoff schemes with latencies less than 50 ms to ensure that real-time applications such as VoIP can be performed without service degradation. Flexible key management schemes assure that security is maintained during handoff.
Source of Information : Elsevier Wireless Networking Complete
The WiMAX product certifi cation program ensures interoperability between WiMAX equipment from vendors worldwide. The certifi cation program also considers interoperability with (HIPERMAN), the European telecommunication standards institute’s MAN standard.
With its large range and high transmission rate, WiMAX can serve as a backbone for 802.11 hotspots for connecting to the Internet. Alternatively, users can connect mobile devices such as laptops and handsets directly to WiMAX base stations without using 802.11. Mobile devices connected directly can achieve a range of four to six miles, because mobility makes links vulnerable. The WiMAX technology can also provide fast and cheap broadband access to markets that lack infrastructure (fi ber optics or copper wire), such as rural areas and unwired countries. WiMAX can be used in disaster recovery scenes where the wired networks have broken down. It can be used as backup links for broken wired links.
WiMAX can typically support data rates from 500 kbps to 2 Mbps. WiMAX also has clearly defi ned QoS classes for applications with different requirements such as VoIP, real-time video streaming, file transfer, and web traffic. A cellular architecture similar to that of mobile phone systems can be used with a central base station controlling downlink/uplink traffic.
WiMAX is a family of technologies based on IEEE 802.16 standards. There are two main types of WiMAX today: fi xed WiMAX (IEEE 802.16d — 2004) and mobile WiMAX (IEEE 802.16e — 2005). Fixed WiMAX is a point-to-multipoint technology, whereas mobile WiMAX is a multipoint-to-multipoint technology, similar to that of a cellular infrastructure. Both solutions are engineered to deliver ubiquitous high-throughput broadband wireless service at a low cost. Mobile WiMAX uses orthogonal frequency division multiple access (OFDMA) technology which has inherent advantages in latency, spectral efficiency, advanced antenna performance, and improved multipath performance in an NLOS environment. Scalable OFDMA (SOFDMA) has been introduced in IEEE 802.16e to support scalable channel bandwidths from 1.25 to 20 MHz. Release 1 of mobile WiMAX will cover 5, 7, 8.75, and 10 MHz channel bandwidths for licensed worldwide spectrum allocations in 2.3, 2.5, 3.3, and 3.5 GHz frequency bands. Also, next generation 4G wireless technologies are evolving toward OFDMA and IP-based networks as they are ideal for delivering cost-effective highspeed wireless data services.
The WiMAX specifi cation improves upon many of the limitations of the Wi-Fi standard (802.11b) by providing increased bandwidth and stronger encryption.
The 802.16 standard was designed mainly for point-to-multipoint topologies, in which a base station distributes traffic to many subscriber stations that are mounted on rooftops. The pointto-multipoint confi guration uses a scheduling mechanism that yields high efficiency because stations transmit in their scheduled slots and do not contend with one another. WiMAX does not require stations to listen to one another because they encompass a larger area. This scheduling design suits WiMAX networks because subscriber stations might aggregate traffic from several computers and have steady traffic, unlike terminals in 802.11 hotspots, which usually have bursty traffi c. The 802.16 also supports a mesh mode, where subscriber stations can communicate directly with one another. The mesh mode can help relax the LOS requirement and ease the deployment costs for high-frequency bands by allowing subscriber stations to relay traffi c to one another. In this case, a station that does not have LOS with the
base station can get its traffi c from another station. Mobile WiMAX systems offer scalability in both radio access technology and network architecture, thus providing a great deal of flexibility in network deployment options and service offerings. Some of the salient features supported by WiMAX are:
● High data rates: The inclusion of MIMO antenna techniques along with flexible subchannelization schemes, advanced coding, and modulation all enable the mobile WiMAX technology to support peak downlink data rates of 63 Mbps per sector and peak uplink data rates of up to 28 Mbps per sector in a 10 MHz channel.
● QoS: The fundamental premise of the IEEE 802.16 MAC architecture is QoS. It defines service fl ows which can map to DiffServ code points or MPLS flow labels that enable end-to-end IP-based QoS. Additionally, sub-channelization and MAP-based signaling schemes provide a flexible mechanism for optimal scheduling of space, frequency, and time resources over the air interface on a frame-by-frame basis.
● Scalability: Mobile WiMAX is designed to be able to scale to work in different channelization from 1.25 to 20 MHz to comply with varied worldwide requirements as efforts proceed to achieve spectrum harmonization in the longer term.
● Security: Support for a diverse set of user credentials exists including SIM/USIM cards, smart cards, digital certifi cates, and user name/password schemes based on the relevant extensible authentication protocol (EAP) methods for the credential type.
● Mobility: Mobile WiMAX supports optimized handoff schemes with latencies less than 50 ms to ensure that real-time applications such as VoIP can be performed without service degradation. Flexible key management schemes assure that security is maintained during handoff.
Source of Information : Elsevier Wireless Networking Complete
Saturday, August 11, 2012
IEEE 802.16
The IEEE 802.16 standard delivers performance comparable to traditional cable, DSL, or T1 offerings. The principal advantages of systems based on 802.16 are multifold: faster provisioning of service, even in areas that are hard for wired infrastructure to reach; lower installation cost; and ability to overcome the physical limitations of the traditional wired infrastructure. 802.16 technology provides a flexible, cost-effective, standard-based means of filling gaps in broadband services not envisioned in a wired world. For operators and service providers, systems built upon the 802.16 standard represent an easily deployable “ third pipe ” capable of delivering flexible and affordable last-mile broadband access for millions of subscribers in homes and businesses throughout the world [3, 4] .
The 802.16a is an extension of the 802.16 originally designed for 10 – 66 GHz. It covers frequency bands between 2 and 11 GHz and enables NLOS operation, making it an appropriate technology for last-mile applications where obstacles such as trees and buildings are often present and where base stations may need to be unobtrusively mounted on the roofs of homes or buildings rather than towers on mountains.
The 802.16a has a range of up to 30 miles with a typical cell radius of 4 to 6 miles. Within the typical cell radius NLOS performance and throughputs are optimal. In addition, the 802.16a provides an ideal wireless backhaul technology to connect 802.11 WLAN and commercial 802.11 hotspots with the Internet. Table 5.18 provides a road map of IEEE 802.16 standards.
Applications of the 802.16 are cellular backhaul, broadband on-demand, residential broadband, and best-connected wireless service. The 802.16 delivers high throughput at long ranges with a high spectral efficiency. Dynamic adaptive modulation allows base stations to trade off throughput for range. The 802.16 supports flexible channel bandwidths to accommodate easy cell planning in both licensed and unlicensed spectra worldwide. The 802.16 includes robust security features and QoS needed to support services that require low latency, such as voice and video. The 802.16 voice service can either be TDM voice or VoIP. Privacy and encryption features are also included to support secure transmission and data encryption.
The Worldwide Interoperability for Microaccess, Inc . (WiMAX) forum, an industry group, focused on creating system profi les and conformance programs to ensure operability among devices based on the 802.16 standard from different manufacturers.
Source of Information : Elsevier Wireless Networking Complete
The 802.16a is an extension of the 802.16 originally designed for 10 – 66 GHz. It covers frequency bands between 2 and 11 GHz and enables NLOS operation, making it an appropriate technology for last-mile applications where obstacles such as trees and buildings are often present and where base stations may need to be unobtrusively mounted on the roofs of homes or buildings rather than towers on mountains.
The 802.16a has a range of up to 30 miles with a typical cell radius of 4 to 6 miles. Within the typical cell radius NLOS performance and throughputs are optimal. In addition, the 802.16a provides an ideal wireless backhaul technology to connect 802.11 WLAN and commercial 802.11 hotspots with the Internet. Table 5.18 provides a road map of IEEE 802.16 standards.
Applications of the 802.16 are cellular backhaul, broadband on-demand, residential broadband, and best-connected wireless service. The 802.16 delivers high throughput at long ranges with a high spectral efficiency. Dynamic adaptive modulation allows base stations to trade off throughput for range. The 802.16 supports flexible channel bandwidths to accommodate easy cell planning in both licensed and unlicensed spectra worldwide. The 802.16 includes robust security features and QoS needed to support services that require low latency, such as voice and video. The 802.16 voice service can either be TDM voice or VoIP. Privacy and encryption features are also included to support secure transmission and data encryption.
The Worldwide Interoperability for Microaccess, Inc . (WiMAX) forum, an industry group, focused on creating system profi les and conformance programs to ensure operability among devices based on the 802.16 standard from different manufacturers.
Source of Information : Elsevier Wireless Networking Complete
Tuesday, August 7, 2012
Performance of a Bluetooth Piconet in the Presence of IEEE 802.11 WLANs
Due to its global availability, the 2.4 GHz ISM unlicensed band is a popular frequency band to low-cost radios. Bluetooth and the IEEE 802.11 WLAN both operate in this band. Therefore,
it is anticipated that some interference will result from both these systems operating in the
same environment. Interference may lead to significant performance degradation. In this section, we evaluate Bluetooth MAC layer performance in the presence of neighboring Bluetooth piconets and neighboring IEEE 802.11 WLANs.
A packet collision occurs when a desired Bluetooth packet [15 – 17] overlaps the interfering packets in time and frequency. In Bluetooth, the duration of a single slot packet is 366 ms and the duration of the slot is 625 ms. The time between the end of the transmission of the packet
and the start of the next slot is the idle time. Similarly, the duration of one 802.11 packet traffic time includes packet transmission time and a back off period.
To simplify the analysis, we make the following assumptions:
● The link is continuously established and the collocated systems are sufficiently close to each other such that the Bluetooth packet will be corrupted completely by the interference packets even if they overlap by a single bit.
● The desired Bluetooth packet will not be destroyed by another piconet if it is hit during the idle time.
● The desired Bluetooth packet will not be destroyed by an IEEE 802.11 network during the IEEE 802.11 backoff period.
● In Bluetooth, the hopping patterns are 100% uncorrelated.
● For a long enough observation time, a given transmitter uses the 79 hopping channels equally.
● There are also 79 channels spaced 1 MHz apart in the IEEE 802.11 FH system.
● Each station’s signal hops from one modulating frequency to another in a predetermined pseudo-random sequence.
The collision probability of Bluetooth to the IEEE 802.11 FH system is 1/79. In the IEEE 802.11 DS, the data stream is converted into a symbol stream which spreads over a relatively wide band channel of 22 MHz, so the interference on a Bluetooth packet from IEEE 802.11 DS system is much higher than that from the 802.11 FH system. It is because the bandwidth of a channel in DS is 22 times as wide as Bluetooth one channel. The collision probability of Bluetooth to the IEEE 802.11 DS system is 22/79.
Source of Information : Elsevier Wireless Networking Complete
it is anticipated that some interference will result from both these systems operating in the
same environment. Interference may lead to significant performance degradation. In this section, we evaluate Bluetooth MAC layer performance in the presence of neighboring Bluetooth piconets and neighboring IEEE 802.11 WLANs.
A packet collision occurs when a desired Bluetooth packet [15 – 17] overlaps the interfering packets in time and frequency. In Bluetooth, the duration of a single slot packet is 366 ms and the duration of the slot is 625 ms. The time between the end of the transmission of the packet
and the start of the next slot is the idle time. Similarly, the duration of one 802.11 packet traffic time includes packet transmission time and a back off period.
To simplify the analysis, we make the following assumptions:
● The link is continuously established and the collocated systems are sufficiently close to each other such that the Bluetooth packet will be corrupted completely by the interference packets even if they overlap by a single bit.
● The desired Bluetooth packet will not be destroyed by another piconet if it is hit during the idle time.
● The desired Bluetooth packet will not be destroyed by an IEEE 802.11 network during the IEEE 802.11 backoff period.
● In Bluetooth, the hopping patterns are 100% uncorrelated.
● For a long enough observation time, a given transmitter uses the 79 hopping channels equally.
● There are also 79 channels spaced 1 MHz apart in the IEEE 802.11 FH system.
● Each station’s signal hops from one modulating frequency to another in a predetermined pseudo-random sequence.
The collision probability of Bluetooth to the IEEE 802.11 FH system is 1/79. In the IEEE 802.11 DS, the data stream is converted into a symbol stream which spreads over a relatively wide band channel of 22 MHz, so the interference on a Bluetooth packet from IEEE 802.11 DS system is much higher than that from the 802.11 FH system. It is because the bandwidth of a channel in DS is 22 times as wide as Bluetooth one channel. The collision probability of Bluetooth to the IEEE 802.11 DS system is 22/79.
Source of Information : Elsevier Wireless Networking Complete
Friday, August 3, 2012
MAID
The concept of MAID (Massive Array of Inactive Disks) has been recently introduced. It refers to a collection of low-cost SATA (or even PATA) disks drives that are not active until they are accessed. Once a disk is going to be accessed, it is activated. This results in a lower acquisition cost and a lower operation cost, owing to the reduced electrical consumption. Of course, response time is heavily increased as compared with active disks, since the typical starting time of a disk is about 10 seconds. MAID can be used wherever access time is not a key factor; for instance, a MAID can serve as a cache to a tape library or as an alternative to tapes.
Intelligent Discs
We must also discuss a proposal from University of California at Berkeley researchers. The proposal addresses making use of the intelligence embedded within today’s disks. They call the proposal Intelligent Disks.
The rationale is straightforward: as the industry migrates towards higher-level interfaces such as SCSI or FC-AL, disk drives needed to embed greater processing power, nowadays typically making use of a 32-bit microprocessor and several megabytes of memory. The suggestion is simply to move some file system or database functionality onto this microprocessor.
Clearly, there is a question of balance; during IBM’s introduction of the S/360, processors were relatively slow, and thus there was substantial pressure to off-load tasks from them. This lead to the use of intelligent disk controllers allowing disk searches to be done according to specified criteria (the interface was called CKD or ECKD). As time passed, minicomputers and early microprocessor systems became rather higher performance and cheap, driving the adoption of simple, low-cost disk interfaces such as SMD and later ESDI. These interfaces had limitations, and once more an intelligent interface, this time SCSI, was introduced to overcome them, necessitating the presence of microprocessors and memory in the disk drives themselves.
Choosing commodity low-cost processors provided much more computer power than was needed by the task, but kept costs down.
The success of this approach, however, does not rest on hardware technology but rather requires that the industry adopt the standards, that operating systems support it, and—perhaps most significantly—that the major database vendors also adopt it.
Source of Information : Elsevier Server Architectures
Intelligent Discs
We must also discuss a proposal from University of California at Berkeley researchers. The proposal addresses making use of the intelligence embedded within today’s disks. They call the proposal Intelligent Disks.
The rationale is straightforward: as the industry migrates towards higher-level interfaces such as SCSI or FC-AL, disk drives needed to embed greater processing power, nowadays typically making use of a 32-bit microprocessor and several megabytes of memory. The suggestion is simply to move some file system or database functionality onto this microprocessor.
Clearly, there is a question of balance; during IBM’s introduction of the S/360, processors were relatively slow, and thus there was substantial pressure to off-load tasks from them. This lead to the use of intelligent disk controllers allowing disk searches to be done according to specified criteria (the interface was called CKD or ECKD). As time passed, minicomputers and early microprocessor systems became rather higher performance and cheap, driving the adoption of simple, low-cost disk interfaces such as SMD and later ESDI. These interfaces had limitations, and once more an intelligent interface, this time SCSI, was introduced to overcome them, necessitating the presence of microprocessors and memory in the disk drives themselves.
Choosing commodity low-cost processors provided much more computer power than was needed by the task, but kept costs down.
The success of this approach, however, does not rest on hardware technology but rather requires that the industry adopt the standards, that operating systems support it, and—perhaps most significantly—that the major database vendors also adopt it.
Source of Information : Elsevier Server Architectures
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