CTN Issue: March 2012

1. Evolution of the Standards for Packet Network Synchronization

The evolution of telecom networks away from the traditional circuit switched structures towards the evolving next generation network with packet switching has changed the model from one of a carefully planned and engineered network towards one in which there is a greater expectation of automatic, self-configured operation a plug and play model. This expectation now also extends to the distribution of synchronization information ˆ frequency, time and phase ˆ over the network. This new expectation widens the scope of interest in network synchronization beyond specialists to the wider audience of telecommunications engineers in general. A new series of standards has recently been developed to address the issue of synchronization transport over packet networks, coming out of both the ITU (G-82xx series) and IEEE (IEEE 1588). A recent article by Ferrant and Ruffini summarizes the work done by ITU-T Q13/15 in developing these standards. Through the process of describing the roadmap of this family of standards, the article walks the reader through the various issues that arise in this new manner of sync transport. Specific technical issues, both theoretical as well as practical aspects brought up by industry, are mentioned in the context of various documents, giving the reader the option of following up on specific issues based on their specific interests. In particular, future work addressing time and phase transport, relevant for wireless networks as well as many emerging applications, is also described. Readers interested in further information on this topic may continue on to more detailed articles in the same issue.

Title and author(s) of the original paper in IEEE Xplore:
Title: Evolution of the Standards for Packet Network Synchronization
Author: Jean-Loup Ferrant and Stefano Ruffini
This paper appears in: IEEE Communications Magazine
Issue Date: February 2011

2. A General Framework for Performance Analysis of Space Shift Keying (SSK) Modulation in the Presence of Gaussian Imperfect Estimations

Spatial Modulation (SM) is a promising multiple-input-multiple-output (MIMO) transmission technique that utilizes the spatial information in a novel fashion. At each time instance, only a single transmit antenna is activated among the set of existing transmit antennas to transmit either a fixed power (no constellation symbol), as in Space Shift Keying (SSK), or a constellation data symbol from the activated transmit antenna, as in conventional SM. As compared to other MIMO techniques, SM is shown to have several advantages, including complete avoidance of inter-channel interference (ICI), relaxed inter-antenna synchronization requirements, low receiver complexity and the use of a single RF chain at the transmitter. Furthermore, with a moderate number of transmit antennas, it has been observed that SM can achieve better error performance than STC (space-time coding) and V-BLAST (Vertical-Bell Lab Layered Space-Time) when perfect channel state information (CSI) is available at the receiver.

The major censure about SM is its performance in real-time transmission and robustness to channel estimation errors due to its working principle. Specifically, some researchers anticipate that the SM system performance will degrade significantly in the presence of imperfect channel knowledge at the receiver due to the mapping of information bits into the index of transmit antennas. This work sheds light on this matter and provides error analysis with the assumption of imperfect channel state information at the receiver side.

Reported results demonstrate some interesting implications on the practical use of SM in the current and future wireless networks. It has been observed that the SM scheme is quite robust to channel estimation errors as compared to STC and VBLAST and requires less training symbols.

Title and author(s) of the original paper in IEEE Xplore:
Title: A General Framework for Performance Analysis of Space Shift Keying (SSK) Modulation in the Presence of Gaussian Imperfect Estimations
Author: Salama Said Ikki and Raed Mesleh
This paper appears in: IEEE Communications Letters
Issue Date: February 2012

3. Spectrum Monitoring during Reception in Dynamic Spectrum Access Cognitive Radio Networks

If a frequency band has primary and secondary users, then the cognitive radios of the secondary users must monitor the band and cease to transmit if a primary user's radio begins to transmit. Traditional methods require the secondary users to not transmit while they monitor for the emergence of primary user signals. This article proposes and analyzes techniques by which the secondary radios can continue transmitting during monitoring.

Then, if a primary user appears to be present during monitoring using this article's method, traditional methods are used by the secondary user to verify that the primary user is present and stop transmission. This technique reduces the average time between the start of a primary user's transmission and the stopping of the secondary user's transmission and increases the communication efficiency of the secondary radio, thus improving the overall performance of cognitive radio systems.

For an overview on cognitive radios, see an article by Joseph Mitola III and Gerald Q. Maguire, Jr.

Title and author(s) of the original paper in IEEE Xplore:
Title: Spectrum Monitoring During Reception in Dynamic Spectrum Access Cognitive Radio Networks
Author: Steven W. Boyd, J. Michael Frye, Michael B. Pursley and Thomas C. Royster IV
This paper appears in: IEEE Transactions on Communications
Issue Date: February 2012

Statements and opinions given in a work published by the IEEE or the IEEE Communications Society are the expressions of the author(s). Responsibility for the content of published articles rests upon the authors(s), not IEEE nor the IEEE Communications Society.