3
Aug 09

Directional Antennas and Multi-Antenna Systems “note 4”

To improve physical layer performance in a wireless environment, a common technology is to consider directional communications or use multiple antennas on the same communication node. It should be noted that a multi-antenna communication system consists of both RF components and baseband processing.

Directional Antenna
Directional antennas enable directional transmission and reception in a wireless network, and thus have several advantages.
Better spatial reuse efficiency. Since transmission and reception are directional, channel reuse does not need to rely on spacial separation, which significantly improves channel spatial reuse efficiency. This feature helps to increase network capacity.
Lower interference. Directional transmission and reception reduces the collisions and interference among different nodes. This feature improves the QoS and throughput of a network.
Less energy consumption for the same network capacity. For the same transmission range, less transmit power is needed by a directional antenna than an omni-directional antenna. Thus, for the same transmission rate, less interference will produce by a node to other nodes. In other words, this feature not only improves the energy efficiency , but also increases the network capacity.
Better security. Due to directional transmission, eavesdropping becomes much more difficult, and thus enhances security of the network at the physical layer. Directional antennas can be realized in the following methods.
Steerable antenna. In this case, one antenna is used on each node, pointing in a specific direction. For networking with other nodes, the antenna needs to be mechanically or electronically steerable so that the antenna points to the right direction at the right time . Since the process of changing the direction of a steerable antenna may be slower than ad hoc networking needs, it is not always a good choice for WMNs.

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3
Aug 09

Cooperative Diversity and Cooperative Communications ”Note 5”

Tradeoff of power. Since one signal needs to be sent to at least two different nodes, more power is needed to send data from source to destination. On the other hand, with diversity, the transmit power at each node can be smaller than in the noncooperative mode. Thus, it is necessary to develop a power allocation algorithm such that minimum transmit power is used to maintain the user cooperative diversity.
Tradeoff of transmission rate. In cooperative communication, a node needs to relay other nodes’ data and also transmit its own data. Thus, its transmission rate is reduced. However, due to diversity, channel coding rates can be higher, which increases the transmission rate. Thus, the actual transmission rate may not be reduced. In order to keep the transmission rate as high as possible, we need to consider tradeoff between diversity and reduced chance of transmission.
• Interference. With cooperative diversity, interference may also be increased, because the same signal is sent more than once in the network. However, diversity may reduce the transmit power level, which can compensate for the increased interference.
Cooperation assignment scheme. This is concerned with finding other cooperative nodes for each node so that diversity can be achieved. In a one-hop infrastructure based network, cooperation assignment may be just a simple task. However, in a multihop distributed network such as WMNs, cooperation assignment is rather complicated, because it has to take into account many factors such as diversity gain, power, interference, and even fairness among nodes.
New requirements on network nodes. Although diversity can be achieved through cooperative communications, algorithms are still needed to retrieve original data from multiplexed signals. This requires additional processing power on either transmitter or receiver. The functionality of cooperative communications may also need change of hardware in each node.

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3
Aug 09

Physical Layer “note 3”

          Physical layer techniques advance rapidly as communication theories, digital signal processing algorithms, RF technologies, and circuit design for wireless communications quickly evolve. These techniques mainly focus on three directions: increasing transmission rate, improving error resilience capability in a wireless environment, and enhancing reconfigurability and software controllability of radios. In order to increase the capacity of wireless networks, various high-speed physical techniques have been invented. For example, orthogonal frequency division multiplexing (OFDM) has significantly increased the speed of IEEE 802.11 from 11 Mbps to 54 Mbps. A much higher transmission rate can be achieved through Ultra-Wideband (UWB) techniques. However, UWB is only applicable to short-distance applications such as wireless personal area networks (WPANs).

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2
Aug 09

Characteristics “Note 2”

• Multihop wireless network: One incentive to develop WMNs is to extend the coverage range of current wireless networks without sacrificing the channel capacity. Another major objective of WMNs is to provide nonline-of-sight (NLOS) connectivity among users without direct line-of-sight (LOS) links. To meet these requirements, mesh-style multihopping is indispensable , which facilitates higher throughput without sacrificing effective radio range via shorter link distances, less interference between nodes, and more efficient frequency reuse. • Support for ad hoc networking, and capability of self-forming, self-healing, and self-organization:Ad hoc networking enhances network performance, such as flexible network architecture, easy deployment and configuration, fault tolerance, and mesh connectivity, i.e., multipoint-to-multipoint communications. Due to these features, WMNs have low upfront investment requirement, and the network can grow gradually as needed.

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2
Aug 09

Wireless Mesh Networks “note 1”

          Wireless Mesh Networks (WMNs) are one of the key technologies which will dominate wireless networking in the next decade. They will help to realize the long-lasting dream of network connectivity anywhere anytime with simplicity and low cost. Accordingly they will play a major role within the next generation Internet. Their capability for self-organization significantly reduces the complexity of network deployment and maintenance, and thus, requires minimal upfront investment.

          These networks consist of simple mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs) wireless personal area networks, (WPANs), and wireless metropolitan area networks (WMANs). These networks deliver wireless services to a large variety of applications in personal, local, campus, and metropolitan areas.

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23
Jul 09

Green Packet Continues to Make its Mark in WiMAX – Part II

With Long Term Evolution (LTE) to be launched in the near future, do you think that Green Packet will eventually incorporate LTE into its strategy? Being a next generation broadband solutions provider, we have been catering for all the broadband networks that has emerged over the years, both IP-based and GSM networks. LTE is an evolution from the GSM network to an all IP-based network. Naturally, we will support LTE as well. In fact, we are currently involved in R&D efforts in order for our solutions to support LTE.

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23
Jul 09

Green Packet Continues to Make its Mark in WiMAX I

Wimax News catches up with Green Packet, a leading solutions developer in the 4G market, in Part I of this exclusive interview with the company’s Senior General Manager, Kelvin Lee:Can you please introduce your company ? Green Packet Solutions is part of the Green Packet Berhad group of companies which is a leading developer of Next Generation Mobile Broadband and Networking Solutions.  We were founded in the Silicon Valley in 2000, and since have expanded our global footprint to include offices in Kuala Lumpur (Headquarters), Singapore, Shanghai, Taiwan, Australia, Bahrain and Bangkok.   If I was to summarize our offering I would say: Green Packet Solutions empowers operators to improve ARPU via leading edge carrier-grade connectivity solutions and interoperability-tested WiMAX Modems. Green Packet Solutions’ products offer best-in-class performance and are of the highest quality, ensuring our customers are ALWAYS BEST CONNECTED!  With our R&D centres located in USA, Shanghai, and Taiwan, we are on the edge of new developments in 4G (particularly WiMAX and LTE), as well as software advancement. Green Packet Solutions’ presence around the world proves we are a company with global capabilities which can localize to suit individual markets.  Additionally, industry players can leverage on Green Packet Solutions’ strategic alliances in the telecommunications industry to strengthen their own place in the ecosystem.

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