Institute for Systems Research
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Item An Adaptive Hybrid FEC/ARQ Protocol Using Turbo Codes for Multi-Media Transmission of ATM over Wireless Networks(1997) Chan, Wai-Chung; Geraniotis, Evaggelos A.; ISR; CSHCNThis paper describes a type-II adaptive hybrid FEC/ARQ protocol using turbo codes for both voice and data services.Recently, a powerful family of error correcting codes using parallelconcatenated convolutional codes is introduced. Near-Shannon-limitis achievable by such codes. For example, a bit error rateof $10^{-5}$ can be achieved at $E_b/N_o =$ 0.7~dB using a rate1/2 code or at about 2.5~dB if fewer iterations are used in decoding.Given the promising performance of the codes, it is expected thatthe performance of an adaptive FEC/ARQ protocol employingturbo codes will be better than protocols using other error correcting codes.Rate compatible turbo codes are used in the protocol. Extra parity bitscorresponding to a lower rate turbo code will betransmitted if the previous transmission leads to a decoding error.For real-time services, the number of retransmissions is limited to one soas to limit the delay. For data services, the number of retransmissions is unlimited to provide a reliable communication link.Results in terms of throughput are obtained for the adaptive FEC/ARQ protocol using compatible rate 1/2 and rate 1/4 turbo codes.Item A Methodology for Modeling, Performance Analysis, and Control of ATM Networks with Multi-Media Traffic(1997) Chou, Chih-Hsien; Chan, Wai-Chung; Geraniotis, Evaggelos A.; ISR; CSHCNIn this paper we review recent advances in developing a methodology for traffic modeling, performance evaluation, and control of ATM networks that can be used to support several aspects of Task 4.3 of the ATIRP project. Our methodology includes model matching and validation for multi-media traffic, analytical approximation techniques for time-efficient and accurate evaluation of end-to-end as well as intermediate node performance measures of multi-hop networks, and optimization of control (resource allocation) schemes.Item Medium Access Protocols for Interconnecting ATM and Wireless Networks(1997) Chan, Wai-Chung; Geraniotis, Evaggelos A.; ISR; CSHCNThe current trend in modern telecommunication is that most of the traffic (CBR, VBR and ABR, real-time and delay-insensitive) in the fixed broadband networks will be carried by fixed-length packets. It is desirable to extend the services to wireless networks as well. However, one major difficulty in wireless networks is the limited spectrum available. Another difficulty is that the bit error rate (BER) of the wireless channel is typically much higher than that of the channels of the wireline broadband networks. The latter problem is amplified for military wireless networks that experience substantial link interference (e.g., multipath fading, other-user interference jamming). Therefore, we can only expect that the same services are being carried in a similar fashion but with a lower source rate. In this paper, a medium access protocol for interconnecting ATM and wireless networks is discussed, followed by some alternatives, and other issues pertaining to guaranteeing low BER. This research was conducted in support of Task 1.1 of the ATIRP project during FY 96 and continues under Task 4.3 for FY 97.Item New Array Processing Algorithms for Maximizing Capacity of Multi-Media Spread-Spectrum Multi-Access Communications(1997) Fruth, Frank; Liu, Shang-Chieh; Geraniotis, Evaggelos A.; ISR; CSHCNAdaptive arrays are a key technique for maximizing the capacity of wireless multimedia CDMA networks. In this paper, we present two approaches for blind adaptive weight control in CDMA environment which offer low implementation complexity. The first method is based on the concept of a self-generated reference signal combined with traditional LMS and RLS adaptive algorithms. The second method is an eigenspace algorithm which is based on eigenvalue decomposition and interference cancellation. Simulation results for both methods are presented for a low- mobility multipath environment and show reliable convergence with significant SINR improvements in the reception of a desired signal.Item Optimal Policies for Handoff and Channel Assignment in Networks of LEO Satellites Using CDMA(1996) Chang, Yu-Wen; Geraniotis, Evaggelos A.; ISR; CSHCNIn this paper, we formulate the combined handoff and channel assignment problems in a CDMA LEO satellite network as a reward/cost optimization problem. The probabilistic properties of signals and traffics in cells are used to formulate a finite- horizon Markov decision process. The optimal policy is obtained by minimizing a cost function consisting of the weighted sum of the switching costs and blocking costs of traffics subjects to a bit-error-rate or outage probability constraint. A backward induction algorithm is applied to derive the optimal policy. Performance of the optimal policy and the direct threshold policy are compared.Item Optimal Strategies for Admitting Voice and Data Traffic in Networks of Leo Satellites Using CDMA(1995) Geraniotis, Evaggelos A.; Chang, Yu-Wen; Yang, Wen-Bin; ISR; CSHCNEfficient policies are derived for admitting voice and data traffic into networks of low-earth-orbit (LEO) satellites using code-division multiple-access (CDMA) with direct-sequence spread- spectrum (DS/SS) signaling. The satellites act as bent-pipes; no on-board processing or inter-satellite links are present. Dual satellite diversity is used to mitigate the effects of shadowing. The policies assume a movable boundary form, allocate optimally the CDMA capacity (PN codes) to voice and data users, and can increase significantly the number of users served while satisfying their bit error rate (BER) requirements. A modified version of our policies can handle two classes of data users: one with high priority which requires real-time delivery and another with low priority that can be queued; the BER requirements of the two data types may differ.Item Voice, Data, and Video Integration for Multi-Access in Broadband Satellite Networks(1993) Ghaffari, Behzad; Geraniotis, Evaggelos A.; ISR; CSHCNMulti-media integration of broadband services in a broadband satellite network is considered. Voice, data, video teleconferencing, and television with broad range of service (bit) rates are multiplexed through a broadband satellite, channel in a multiple-access fashion. Large (but finite) population sizes are considered with arrivals modeled by binomial distributions. A two-state minisource model is used for voice signals. For video, variable rate interframe coding is utilized to reduce the bandwidth requirements, and Markov phase processes model the modulation of the rates of the video teleconferencing and television signals.Among these services, video and voice are real-time signals and can not tolerate large random delays. In our attempt to satisfy this, video and voice use the Synchronous Transfer Mode (STM) with a frame structure, while the data users (with their bursty traffic) send (and retransmit, if necessary) their packets randomly within a frame. The video and voice users make their schedules in advance by using a pre- assigned slot (status slot). The first portion of a frame is assigned to the variable rate video users, while the variable rate voice users fill up the last portion of the frame. Data packets fill up the remaining slots between these two movable boundaries in a random-access fashion. In this protocol, the delay introduced by the satellite is taken into consideration. This multiple-access integration protocol is optimized with respect to performance measures, such as the blocking probabilities for voice and video, the average delay for data, and the average throughput for voice, video, and data.
Item The Probability of Multiple Correct Packet Receptions in Direct- Sequence Spread-Spectrum Networks(1993) Geraniotis, Evaggelos A.; Wu, J.; ISR; CSHCNIn this report, we provide an accurate analysis of the probabilities P(l, m-l K), l = 0,1, ..., m and mK, of exactly l correct packet receptions in a group of m receivers, given that K packets are transmitted simultaneously from users employing direct-sequence spread-spectrum (DS/SS) signaling schemes. This quantity is essential for the design and performance evaluation of protocols for admission control, dynamic code allocation of multiple-access spread-spectrum packet radio networks; specific applications include networks of LEO satellites and multi-rate multi-media communications using CDMA (code-division multiple- access) techniques. The evaluations are carried out for DS/SS networks employing BPSK modulation with coherent demodulation and convolutional codes with Viterbi decoding. systems with geographically dispersed receivers and systems with colocated receivers are considered.First the exact multireception probabilities for synchronous uncoded systems are evaluated at the bit level; these results are essential for checking the accuracy of the other approximations used here. Our results establish that the Independent Receiver Operation Assumption (IROA) yields very good approximations whose accuracy increases as the number of chips per bit N increases. The IROA accuracy is not as satisfactory for colocated receivers when Eb/No is small; for this case we develop an approximation based on the Guassian multivariate distribution, which is ore accurate than the IROA. Extensive comparisons of the exact expressions with the Guassian and the IROA approximations are conducted. For convolutional code systems, we derive the multireception packet probabilities following a new approach, the Joint First Error Event Approximation (JFEEA), which is based on the lower bound of the probabilities of all-correct packet receptions and the moments of random variables. We compare this approximation with the IROA and observe good agreement between the two.
Item Admission Policies for Integrated Voice and Data Traffic in CDMA Packet Radio Networks(1993) Yang, W-B.; Geraniotis, Evaggelos A.; ISR; CSHCNIn this report, we derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code-division multiple-access (CDMA) with direct- sequence spread-spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. Our admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized in longer-term. In addition, new data arrivals are rejected, if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then a value-iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies can be employed by either terrestrial or satellite CDMA networks and are currently being extended to networks of LEO satellites and multi-rate multi-media CDMA communications.Item Channel Holding Time Distribution in a Hybrid Satellite and Cellular Communication System(1993) Wu, T-H.; Geraniotis, Evaggelos A.; ISR; CSHCNThis paper evaluated the distribution of channel holding time in a hybrid satellite and cellular communication system. The channel holding time is defined as the time duration between the instant that a channel is assigned to a call and the instant it is released either upon the completion of a call or a upon the completion of a cell (or satellite footprint) boundary crossing by a mobile. Out hybrid system consists of three levels of cells - microcell, macrocell, and satellite footprint. The distribution of channel holding time for each cell level is analyzed by using a distinct system model. The results show that a negative exponential distribution is an appropriate approximation of the channel holding time in our system. This provides a very useful system parameter in multi-layer cellular systems.