Behnam Kamali

An overview of VHF civil radio network and the resolution of spectrum depletion

The spectral capacity of VHF aeronautical radio is rapidly reaching saturation in the United States and in Europe. A key functional objective for any future civil aviation communications technology is providing relief to the current spectral congestion. This article provides a review on the existing national and global aeronautical radio networks. The spectrum depletion problem is described. Recent developments in narrowband and wideband digital communications for potential applications in civil aviation are discussed. Comments are made on critical issues that must be considered when selecting a communication technology for aeronautics which addresses the spectral congestion problem and simultaneously supports transformation to a long term network centric solution. Recommendations are made on some possible communication technologies that may bring about short-term resolution to VHF spectrum depletion without requiring major changes in ground infrastructure or on-board avionics.

Belief propagation decoding of Reed-Solomon codes; a bit-level soft decision decoding algorithm

In this article we propose the application of Belief Propagation (BP) algorithm as a novel bit-level soft decision decoding (SDD) technique for Reed-Solomon (RS) codes. A brief tutorial on Belief Propagation algorithm is presented. A central issue in the application of BP algorithm to decoding RS codes is the construction of a sparse parity check matrix for the binary image of the code. It is demonstrated that Vardys technique may be applied to find a sparse parity check matrix for RS codes. However, this technique is not applicable to all cases. The BP algorithm is applied to two test codes. In one case, simulation models show that the BP algorithm outperforms the hard decision Euclidean decoding by more than 2 dB of additional coding gain. The results with the second test code are not as promising.

Development of an undergraduate structured laboratory to support classical and new base technology experiments in communications

This paper describes an effective method of teaching a communications laboratory course that supports classical as well as new base technology experiments to undergraduate electrical engineering students. Primarily, experiments dealing with the design of the basic building blocks of analog and digital communications systems are targeted, which provides an opportunity for the student to become familiar with various signal processing techniques applied in modern communications systems, to learn how to operate the communication laboratory test equipment, and to obtain exposure to some hardware/software design and implementation of these subsystems. The second level of experimentation involves a small system in which discrete or integrated devices are used to build small systems. Level three involves experimentation with a complete communications system, such as a fiber optics communications system or a simulated satellite link. Four sample experiments are described in some detail. >

Understanding WiMAX: An IEEE-802.16 Standard-Based Wireless Technology

Worldwide Interoperability for Microwave Access (WiMAX) is an IEEE 802.16 standard-based broadband cellular wireless solution in which orthogonal frequency division multiple access (OFDMA) is the method of sharing communication resources among large numbers of users. This is in contrast with multiple access technologies such as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) that were dominant in 1G (first generation cellular systems), 2G, 2.5G, and 3G cellular networks. As the demand for wireless communications grows almost exponentially, the ability to access these networks becomes an important commodity. This is particularly the case in cellular networks where the demand for broadband access is pushing the industry to advance into the next generation of wireless mobile networks.

On selection of proper IEEE 802.16-based standard for Aeronautical Mobile Airport surface Communications (AeroMACS) application

A new aviation-specific transmission technology based on the WiMAX (Worldwide Interoperability for Microwave Access) IEEE 802.16e-based standard; over a newly available C-band allocation (5091–5150 MHz), has been recently recommended for the airport surface wireless communications network now known as Aeronautical Mobile Airport Communications System (AeroMACS). The proposed standards will be used to support fixed and mobile ground to ground applications and services. It has been established that no technical obstacle exists that would prevent the application of WiMAX networks to AeroMACS. In this article WiMAX networks and some of their salient features are briefly reviewed. The challenges of broadband radio communications through airport surface channels are discussed. A major concern about deployment of AeroMACS over the 5091–5150 MHz band is interference to co-allocated applications such as the Mobile Satellite Service (MSS) feeder link. This limits the power levels that are allowed for AeroMACS networks. We propose an investigation into the feasibility of the application of IEEE 802.16j Amendment (relay-based multi-hop network) to AeroMACS. The potential benefits of multihop relay configuration for AeroMACS networks are identified. Perhaps the most relevant benefit of the multihop relay configuration to AeroMACS is the flexible and cost effective radio range extension that it provides for airport areas shadowed by large constructions and natural obstacles without raising the required network power levels.

Comparison of duobinary and 4-level continuous phase frequency shift keying signals for narrowband land mobile radio applications

The bit error rate performance of partial-response duobinary continuous-phase frequency shift keying (CPFSK), and full-response 4-level CPFSK are compared under the condition of equal RF spectral occupancy and equal data rate, for both Gaussian and Rayleigh fading channels. Incoherent limiter-discriminator detection is assumed for all cases. The spectral efficiency requirements of the FCC, for the allocated 220-222 MHz band for land mobile communications, are used to establish the system specifications. It is shown that 4-level CPFSK system significantly outperforms the 3-level duobinary CPFSK. This is due to the fact that the receiver bandwidth may be lowered for 4FSK thereby higher frequency deviation can be achieved resulting in higher SNR at the receiver which outweighs the noise margin advantage of duobinary system. Simulation systems are designed to measure the performance for both static and Rayleigh-fading narrowband channels.

Some new outlooks on burst error correcting capabilities of Reed-Solomon codes with applications in mobile communications

Some bounds on the required number of parity check symbols for burst error correction are discussed. Equations determining burst error correction capabilities of Reed-Solomon (RS) codes constructed over Galois fields of characteristic two are presented. Tables providing burst error correction capabilities of RS codes constructed over GF(256) and GF(64) are provided. Some applications of RS codes in mobile communications are covered, in particular the selection of the (63,47) RS codes for Cellular Digital Packet Data (CDPD) networks is explained. One legitimate concern regarding the application of RS codes in mobile communications is the computational complexity of the RS codes standard decoding method. Three alternative decoding techniques, suitable for RS codes with low error correcting capability are described

Considerations for improving the capacity and performance of AeroMACS

The Aeronautical Mobile Airport Communications System (AeroMACS) has progressed from concept through prototype development, testing, and standards development and is now poised for the first operational deployments at nine US airports by the Federal Aviation Administration. These initial deployments will support fixed applications. Mobile applications providing connectivity to and from aircraft and ground-based vehicles on the airport surface will occur at some point in the future. Given that many fixed applications are possible for AeroMACS, it is necessary to now consider whether the existing capacity of AeroMACS will be reached even before the mobile applications are ready to be added, since AeroMACS is constrained by both available bandwidth and transmit power limitations. This paper describes some concepts that may be applied to improve the future capacity of AeroMACS, with a particular emphasis on gains that can be derived from the addition of IEEE 802.16j multihop relays to the AeroMACS standard, where a significant analysis effort has been undertaken.

Single Sideband Technologies for Optimization of VHF Aerospace Communications

The highest priority in air travel operation is justifiably placed on flight safety which is critically linked to the availability of reliable communications and navigation systems. The current aeronautical VHF spectrum dedicated to civil aviation communications in the US and the rest of the world isl9 MHz wide. With the 25-kHz commercial AM technology, this band supports 760 radio channels. In the United States, owing to the rise in the number of airplanes in both commercial and general aviation sectors, spectral congestion in the aeronautical VHF band is rapidly becoming a predicament. This article proposes single side band as an alternative technology that enables efficient use of the available spectrum while requiring minimal change in the infrastructure. It is shown that SSB in conjunction the Weaver modulation method presents an economically feasible solution to spectral congestion in VHF aeronautics, with which the system capacity can be increased by a factor of 3, 4, 5, 6, and even 7 (X-factor). Hardware costs increments for implementing either the analog or digital Weaver method are modest among schemes with different X-factors. This implies that it is possible to increase the present capacity of 760 to up to 5320 voice channels; which meets the challenge of required number of civil aviation radio channels for at least two decades.

Error control coding

Error control coding (ECC) is a signal processing technique that protects digital information against transmission and storage errors. Codes that combat randomly distributed errors are called random-error correcting codes. Codes that cope with errors that are clustered together are known as burst-error correcting codes. When data is presented as a stream of binary numbers, bit-oriented codes may be applied. In contrast to this, data might be arranged as words, where each word includes a number of bits. Codes that operate on words are said to be word-oriented codes. The article is limited to linear bit-oriented block codes. >