Peter D. Magill

Enhanced throughput efficiency by use of dynamically variable request minislots in MAC protocols for HFC and wireless access networks

We consider Medium Access Control (MAC) protocols in which minislots are used to request permission to transmit packets of information (voice, data, video, or multi‐media) in the upstream channels, and the information is subsequently transmitted in packet time‐slots allocated by a central controller. Such MAC protocols are currently being considered for Hybrid Fiber‐Coax (HFC) as well as wireless access networks. In this paper, we compare MAC protocols for three cases with regard to request minislots: (1) with no minislots (in this case, the first of a batch of information packets from a station is transmitted in contention mode and also carries with it a reservation request for the remainder of packets in that batch), (2) with fixed number of minislots per frame, and (3) with dynamically variable number of minislots per frame. There is transmission overhead associated with minislots, but there are potential throughput efficiency benefits under a range of traffic mix scenarios. This paper also proposes an algorithm for dynamically varying the number of minislots as a function of the traffic mix. Results based on analytical performance models are presented to compare throughput efficiencies for the three cases stated above. The results show that a MAC protocol with dynamically variable minislots has the highest throughput efficiency amongst the different alternatives mentioned above.

Delivery of >1 Gb/s (digital video, data, and audio) downstream in passband above the 155-Mb/s baseband services on a FTTx full service access network

For low-cost passive optical access networks (PON), we have studied the downstream delivery of an additional >1 Gb/s in the passband above the 155-Mb/s baseband signal. Both signals are transmitted on the same fiber using a single transmitter and a single receiver within the power budgets of ITU-T G983. The passband approach offers a graceful upgrade of a 155-Mb/s baseband system, and is compatible with baseband only optical network unit (ONU). We multiplexed a 155.52-Mb/s baseband signal with QPSK modulated passband>1.2 Gb/s of broadcast DSS digital video channels in the 270-1450-MHz range through a diplexer with minimal degradation. For a passband test-signal, we used an additional 8-Mb/s QPSK modulated 860-MHz carrier. An optical to electrical (O/E) receiver using a p-i-n diode satisfies the need for class B operation as defined in ITU-T G983 (-30 dBm receiver sensitivity) for a 10/sup -10/ bit-error rate. However, an APD based receiver satisfies the power budget needs of ITU-T G983 with /spl sim/5.5 dBo margin for class C operation (-33-dBm receiver sensitivity) for both baseband and passband signals.

System for delivery of broadcast digital video as an overlay to baseband switched services on a fiber-to-the-home access network

For low cost fiber-to-the-home (FTTH) passive optical networks (PON), we have studied the delivery of broadcast digital video as an overlay to baseband switched digital services on the same fiber using a single transmitter and a single receiver. We have multiplexed the baseband data at 155.52 Mbps with digital video QPSK channels in the 270 - 1450 MHz range with minimal degradation. We used an additional 860 MHz carrier modulated with 8 Mbps QPSK as a test-signal. An optical to electrical (O/E) receiver using an APD satisfies the power budget needs of ITU-T document G983.x for both class B and C operations (i.e., receiver sensitivity less than -33 dBm for a 10-10 bit error rate) without any FEC for both data and video. The PIN diode O/E receiver nearly satisfies the need for class B operation (-30 dBm receiver sensitivity) of G983 with FEC in QPSK FDM video. For a 155.52 Mbps baseband data transmission and for a given bit error rate, there is approximately 6 dBo1 optical power penalty due to video overlay. Of this, 1 dBo penalty is due to biasing the laser with an extinction ratio reduced from 10 dBo to approximately 6 dBo, and approximately 5 dBo penalty is due to receiver bandwidth increasing from approximately 100 MHz to approximately 1 GHz. The penalty due to receiver is after optimizing the filter for baseband data, and is caused by the reduced value of feedback resistor of the first stage transimpedance amplifier. The optical power penalty for video transmission is about 2 dBo due to reduced optical modulation index.

Adaptive digital access protocol: new features and performance improvements

This paper reports on a broadband multiple access protocol for bi-directional hybrid fiber-coax (HFC) networks. Referred to here as the enhanced adaptive digital access protocol (ADAPt+TM), it builds upon earlier work to define a medium access control (MAC) protocol amenable to a multiple service environment supporting subscriber access in HFC networks with tree and branch topologies. ADAPt+ efficiently supports different access modes such as synchronous transfer mode (STM), asynchronous transfer mode (ATM), and variable length (VL) native data (e.g., IP, IPX). This enhanced protocol adapts to changing demands for a mix of circuit- and packet-mode applications, and efficiently allocates upstream and downstream bandwidth to isochronous and bursty traffic sources. This paper describes: ADAPt+ for upstream communication and multiplexing/demultiplexing for downstream communication; its applicability to STM, ATM and other native data applications; and performance attributes such as bandwidth efficiency and latency.