It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

The distributed nature and dynamic topology of Wireless Sensor Networks (WSNs) introduces very special requirements in routing protocols that should be met. The most important feature of a routing protocol, in order to be efficient for WSNs, is the energy consumption and the extension of the network's lifetime. During the recent years, many energy efficient routing protocols have been proposed for WSNs. In this paper, energy efficient routing protocols are classified into four main schemes: Network Structure, Communication Model, Topology Based and Reliable Routing. The routing protocols belonging to the first category can be further classified as flat or hierarchical. The routing protocols belonging to the second category can be further classified as Query-based or Coherent and non-coherent-based or Negotiation-based. The routing protocols belonging to the third category can be further classified as Location-based or Mobile Agent-based. The routing protocols belonging to the fourth category can be further classified as QoS-based or Multipath-based. Then, an analytical survey on energy efficient routing protocols for WSNs is provided. In this paper, the classification initially proposed by Al-Karaki, is expanded, in order to enhance all the proposed papers since 2004 and to better describe which issues/operations in each protocol illustrate/enhance the energy-efficiency issues.

Energy-Efficient Routing Protocols in Wireless Sensor Networks: A Survey

A survey of communication/networking in Smart Grids

This article provides a comparative study of different multiple access techniques. It is demonstrated that non-orthogonal approaches have a spectral-power efficiency advantage over orthogonal ones for delay-sensitive applications in fading environments, and that this theoretical advantage can be realized in practice by exploiting recent progress in transmission and detection techniques. The practical aspects of these multiple access techniques are also discussed and compared

Comparison of orthogonal and non-orthogonal approaches to future wireless cellular systems

PEACH: Power-efficient and adaptive clustering hierarchy protocol for wireless sensor networks

This article addresses the issues of next-generation CDMA technologies for B3G wireless communications. To engineer a CDMA system whose performance will no longer be interference-limited, many challenging issues should be tackled, such as novel CDMA code sets, efficient spreading and carrier modulation schemes, and signaling format for high-speed burst traffic. This article reviews our ongoing research on next-generation CDMA technologies. In particular, we propose a new CDMA code design methodology, real environment adapted linearization (REAL), which can generate CDMA code sets with inherent immunity against multipath interference and multiple access interference for both uplink and downlink transmissions. It is also shown that interference-free CDMA can only be implemented with the help of orthogonal complementary codes. The article goes further to reveal that cell-wise capacity for such interference-free CDMA is equal to the number of element codes assigned to each user, making OFDM a natural choice to implement interference-free CDMA. Several other issues of OCC-CDMA, such as its system implementation and performance, are also addressed in this article.

Orthogonal complementary codes for interference-free CDMA technologies

For time-sensitive applications requiring frequent data collections from a remote wireless sensor network, it is a challenging task to design an efficient routing scheme that can minimize delay and also offer good performance in energy efficiency, network lifetime and throughput. In this paper, we propose a new routing scheme, called Shortest Hop Routing Tree (SHORT), to achieve those design objectives through effectively generating simultaneous communication pairs and identifying the shortest hop (closest neighbor) for packet relay. Compared with the existing popular schemes such as PEGASIS, BINARY and PEDAP-PA, SHORT offers the best "energy x delay" performance and has the capability to achieve a very good balance among different performance metrics.

SHORT: Shortest Hop Routing Tree for Wireless Sensor Networks

This paper presents a multicarrier code-division multiple-access (CDMA) system architecture that is based on complete complementary orthogonal spreading codes. The architecture has several advantages as compared to conventional CDMA systems. Specifically, it offers multiple-access interference-free operation in additive white Gaussian noise channels, reduces cochannel interference significantly, and has the potential of higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an ldquooffset stackedrdquo spreading modulation technique. To maintain good performance in the presence of fading, the offset stacked modulator is followed by a quadrature-amplitude modulation map, which is designed to optimize performance in a fading environment. This new modulation scheme also simplifies the rate-matching algorithms that are relevant for multimedia services and Internet Protocol-based applications.

Design of an MC-CDMA System That Uses Complete Complementary Orthogonal Spreading Codes

This paper introduces an approach to generate generalized pairwise complementary (GPC) codes, which offer a uniform interference free windows (IFWs) across the entire code set. The GPC codes work in pairs and can fit extremely power efficient quadrature carrier modems. The characteristic features of the GPC codes include: the set size is 2K, the processing gain is 4NK, and the IFW's width is 8N identically for all codes in a set, where K is the times to perform Walsh-Hadamard expansions and N is element code length of seed complementary codes. Therefore, by using different N, the IFW width of a GPC code set can be adjusted with its set size unchanged. Each GPC code set consists of two code groups, with each having K codes, and they have sparsely and uniformly distributed autocorrelation side lobes and cross-correlation levels outside the IFWs.

Generalized pairwise complementary codes with set-wise uniform interference-free windows

For time-sensitive applications requiring frequent data collections from a remote wireless sensor network, it is a challenging task to design an efficient routing scheme that can minimise delay and also offer good performance in energy efficiency, network lifetime and throughput. In this paper, we propose a new routing scheme, called Shortest Hop Routing Tree (SHORT), to achieve those design objectives through effectively generating simultaneous communication pairs and identifying the shortest hop (closest neighbour) for packet relay. Compared with the existing popular schemes such as PEGASIS, BINARY and PEDAP-PA, SHORT offers the best 'energy × delay' performance and has the capability to achieve a very good balance among different performance metrics.

Hsiao-Hwa Chen

Papers

Orthogonal complementary codes for interference-free CDMA technologies

SHORT: Shortest Hop Routing Tree for Wireless Sensor Networks

Design of an MC-CDMA System That Uses Complete Complementary Orthogonal Spreading Codes

Generalized pairwise complementary codes with set-wise uniform interference-free windows

SHORT: shortest hop routing tree for wireless sensor networks