Seppo J. Halme

An Optimum Retransmission Cut-Off Scheme for Slotted ALOHA

The retransmission cut-off is not needed for a stable operation of slottedALOHA if the new packet generation rate is below a critical limit. Thethroughput never reaches its maximum value if the new packet generation rateis less than this critical limit irrespective of the number of transmissions.The maximum throughput is attained by adjusting the number of transmissions,pertaining to the new packet generation rate exceeding the critical limit.A complete analysis for the new packet generation rate with the properadjustment of the number of transmissions that maximize the channel throughputin a Rayleigh fading channel is executed. A stable operating region in termsof the packet rejection probability and the corresponding number oftransmissions is devised.

Power level selection schemes to improve throughput and stability of slotted ALOHA under heavy load

We propose and analyse three different power selection schemes for slotted ALOHA random access protocol operating under multiple power levels. Through analysis and numerical examples we demonstrate that these schemes can significantly improve the performance of slotted ALOHA, in terms of throughput and stability, under heavy load. The proposed schemes are truly distributive in nature and can be easily implemented in wireless access systems without requiring any centralised control.

Optimizing the Use of Random Access Channels in GSM-GPRS

The random access channels and traffic channels are utilized, respectively, for call establishment and information transmission in the uplink direction (from mobile to base station) of the Global System for Mobile communications (GSM) networks. A call is either rejected or blocked depending on its inability to succeed either in the random access channels or in the traffic channels. The optimum number of random access slots is directly proportional to the average call arrival rate, being independent of the average channel holding time and the number of traffic channels. The number of slots occupied by a given call can be changed dynamically in the newly developed General Packet Radio Service (GPRS) systems. A complete analysis is executed for the traffic channel utilization and call blocking probability with the exact number of random access slots that provide almost zero call rejection probability. The overall call success probability is derived considering call rejection and call blocking probabilities.

Performance analysis of GSM traffic channel capacity with(out) high speed circuit switched data

Analytical techniques for GSM traffic channel capacity analysis are studied. The results are represented for high speed circuit-switched data (HSCSD) traffic channels co-existing with voice traffic channels in a GSM cell. In a GSM system the base station has a finite number of traffic channels, from which one voice terminal occupies one traffic channel. The admission priority for voice services is higher than that of the HSCSD data. On the other hand, one HSCSD terminal can occupy a multiple number of channels if needed, provided that they are available. The HSCSD terminal will release its reserved traffic channels only after the data transmission is completed. The presence of HSCSD services slightly increases the blocking probability of the voice terminals. The results in this paper show the steady-state channel utilization and blocking probability of voice terminals under the constraints where voice terminals occupy one traffic channel at a time and data terminals can occupy multiple number of traffic channels. The results show that for a defined acceptable voice blocking probability, the overall channel utilization increases with the higher number of HSCSD terminals allowed per base station as well as with the higher number of channels allowed to be allocated for each HSCSD terminal. The traffic channel utilization also increases if the acceptable blocking probability for voice terminals is allowed to increase. The analytical model represented herein is general. Therefore, the channel utilization and the voice blocking probability results are calculated both with/without the HSCSD traffic channels. These numerical cases can be obtained by appropriate parameter setting from the same process model.

GPRS-features and packet random access channel performance analysis

Mobile data communications (Internet-mobile communication convergence) seems natural as the popularity of both technologies increase. Our purpose in this article was twofold. First, we reviewed GSM, HSCSD (high speed circuit switched data), GPRS and EDGE (enhanced data rate for GSM evolution). Second, the performance of the packet random access channel (PRACH) was analyzed with respect to quality of service parameters: network access delay, throughput, and failure probability. We derived the overall GPRS traffic channel utilization as a function of the throughput and channel holding time. EDGE introduction will decrease the holding time of GPRS terminals due to multilevel encoding and result in higher throughput. Thus, in order to maintain GPRS channel efficiency, PRACH efficiency must be boosted. Thus packet-capturing is introduced to offset access collisions on (P)RACH and increase its efficiency. We noted that the capture effect decreases with access throughput contrary to access delay and failure rate. These QoS parameters are indicative of network performance, hence crucial for novel network planning.

Efficiency of the GSM-GPRS Air Interface for Real-Time IP Traffic Flows With and Without Packet Dropping

One IP terminal can occupy a single slot or a multiple number of slots within time frames in the GSM and GPRS, respectively. A limited number of radio resources (slots) are allocated in a base station for such IP terminals. If one IP terminal can occupy only one slot discontinuously in a time frame, there is one possibility resorting to all IP terminals to preserve active mode at a time. Thus, the number of accepted call in the GSM is the same as that of the radio resource. Similarly, if one terminal can occupy a multiple number of slots discontinuously/dynamically in a time frame, the number of accepted calls is obtained by dividing the number of radio resources during that time by the maximum allowed number of slots per IP terminal. A burstiness factor is defined for the IP traffic over GSM-GPRS air interface. Traffic channel efficiency with a bursty real-time IP traffic is unacceptably low, especially with the range of acceptable call loss probabilities pertaining to a lower burstiness factor. The channel efficiency can be enhanced and the call loss probability can be suppressed significantly if a higher maximum number of calls is accepted. Allocated radio resources are less than the maximum number of packet transmissions at a time. Therefore, some packets could be dropped from the real-time transmission system. A complete analysis for the real-time IP packet transmission over the single slot GSM and dynamically variable multislot GPRS air interface without packet dropping, and with packet dropping that increases the channel efficiency is executed. Results show that the channel efficiency as well as the packet dropping probability increases with increasing call intensity, maximum number of admitted IP calls and the burstiness factor.

On the use of optical spreading codes to design DWDM systems with reduced FWM crosstalk

Abstract Four-wave mixing (FWM) is a fiber nonlinear effect that limits the maximum reach and minimum channel spacing of a dense wavelength-division multiplexing (DWDM) communication system. We propose an alternative frequency assignment scheme to reduce FWM crosstalk by allocating frequencies to a set of unevenly spaced channels determined by an optical spreading code. This assignment scheme provides several advantages over previously proposed frequency assignment schemes, these include, a reduced optical bandwidth requirements, ease of computing, unlimited channel counts and the complete avoidance of FWM intrachannel crosstalk. Further analysis of the spreading code-based scheme carried out on a 50 GHz spaced 16×2.5 Gbit/s DWDM system, indicates a consistent improvement in Q -factor by over 2 dB compared to similar equal spaced channel DWDM systems.

Components for Optical Fiber Systems

In Chap.2 we reviewed some of the physics of light generation, modulation, and detection, while in Chap.3 we considered the behavior of light as it propagates through the fiber channel. We should now familiarize ourselves with the structure of the actual components that form a communication system, as well as consider the means for coupling them together. Thus, we first review some methods for the fabrication of fibers, and then discuss sources, modulators, and detectors. Coupling problems are treated in Sect.4.5.

Receiver design for laser ranging to satellites

The paper provides a quantitative basis for receiver design whereby timing performance can be evaluated for an arbitrary impulse response using known or measurable system parameters. The analysis accounts for the statistical independence of the multiplication processes of the dynodes as well as the possibility of their non-Poisson behavior. Fixed threshold, constant fraction, and median receivers have been analyzed, and the median receiver has been shown to be significantly superior. Experimental results have been presented which show reasonable agreement with the theory and which confirm the superiority of median timing.

Single channel occupied voice and multi-channel occupied HSCSD over GSM

Random access and traffic channel parts are utilized, respectively, for call establishment and information transmission in the uplink direction, comprising mobile to base station of the Global System for Mobile Communication (GSM) networks. Voice (V) and High Speed Circuit Switched Data (HSCSD) calls use two parallel random access parts and a common traffic channel part where a V call occupies a single traffic channel and a HSCSD call occupies a multiple number of traffic channels. A call is either rejected or blocked if it is unsuccessful either in the random access part or in the traffic channel part. The optimum number of random access slots is directly proportional to the average access arrival rate. According to the specification, four types of retransmission cut-off policies can be executed in the random access part wherein only one type can provide almost zero call rejection probability, pertaining to a limited amount of traffic arrival rate per random access slot. A complete analysis for the traffic channel utilization and call blocking probability for V and HSCSD calls with an exact number of random access slots in collaboration with four different types of retransmission cut-off schemes is introduced. The overall call success probability is devised resorting to call rejection and call blocking probabilities. Results demonstrate that the overall call success probability can be independent of random access part up to a certain call arrival rate if a special type of retransmission cut-off is utilized.