International Journal of Ad Hoc & Sensor Wireless Networks ========================================================== Special Issue for MSN05 PAPER REVIEW FORM ----------------- Title: "ACOS: An Area-based Collaborative Sleeping Protocol for Wireless Sensor Networks" Author(s): Yanli Cai, Minglu Li, Wei Shu and Min-You Wu Reviewer: Antoine Gallais Date To Be Returned: 10 Jan 06 ----------------------------------------------------------------------------- I. NUMERICAL RATING OF THE PAPER: --------------------------------------------------------------------------- Rating Category Your Rating Scale Definition --------------------------------------------------------------------------- Level of 5=Excellent Reader Interest |-----| 4=Very good | 4 | 3=Good |-----| 2=Fair 1=Poor --------------------------------------------------------------------------- Evaluation of Work 5=Excellent work and a major contribution and Contribution |-----| 4=Good solid work of some importance | 4 | 3=Solid work but marginal contribution |-----| 2=Marginal work and very minor contribution 1=Very questionable work and contribution --------------------------------------------------------------------------- Originality 5=Highly original work Novelty |-----| 4=Contains an original contribution | 3 | 3=Somewhat original |-----| 2=Variation of a known concept 1=Complete lack of original ideas --------------------------------------------------------------------------- Practical Utility 5=Excellent |-----| 4=Very good | 3 | 3=Good |-----| 2=Fair 1=Poor --------------------------------------------------------------------------- Quality of 5=Very good Presentation |-----| 4=Basically well written | 4 | 3=Readable |-----| 2=Needs considerable work 1=Unacceptably bad --------------------------------------------------------------------------- Technical 5=Very good Correctness |-----| 4=Good | 3 | 3=Flaws but easy to correct |-----| 2=Some flaws 1=Unacceptably bad --------------------------------------------------------------------------- Overall Rating 5=Strong accept (very good quality) (could be .5) |-----| 4=Accept (good quality) | 4 | 3=Accept if room (marginal quality) |-----| 2=Likely reject (low quality) 1=Definitely reject (has no merit) --------------------------------------------------------------------------- II. SPECIFIC COMMENTS & SUGGESTIONS (to be made available to the author(s)): ------------------------------------ Authors propose an asynchronous area coverage protocol in wireless sensor networks. The idea is to turn redundant sensor nodes into sleep mode to save energy and thus extending the lifetime of the network. Each sensor must decide if it should be active or if it is not required for coverage. The decision is based on the size of the area that is not covered by any other active neighbor (called net area). As long as this size is above a given threshold, the corresponding node must be active (it is the only one able to cover this area). In an asynchronous fashion, nodes get active and then intent to sleep as soon as their activity timer expires. Every message contains both the position and the current timer of the node. Authors show that their solution provides better coverage than two existing solutions while reducing the number of active nodes. Grace to a complete energy model, realistic results are provided concerning the network lifetime. They show that ACOS outperforms both PEAS and PECAS. This work is nicely described and the proposed protocol has some advantages. It can provide different degrees of coverage depending on the value of the threshold. Moreover, authors address an important problem that is not solved by PEAS. The dead node problem (a node fails but is still considered as active by its communication neighbors) is solved by introducing the sleep intending message. Once active nodes have replied, the node can change back to former state if its net area is above the threshold. Unfortunately, it is not precised how to tune the timer in this situation. It may be fixed at its original value or calculated from previously received information. The major drawback of this work is the lack of comparison with best existing solutions. Indeed, outperforming PEAS is not very surprising since ACOS has been designed to solve problems that exist with PEAS (dead node problem, etc.). It is of prime importance that authors compare their work to other contributions that have already addressed the same problems while outperforming PEAS also (see [TG], [JD], [CGSS]). Furthermore, no discussion is made about the communication graph. This feature is particularly important in wireless sensor networks since monitoring reports must reach the sink stations. Therefore, the active nodes set should be connected. Authors use a sensing range r and send messages within a disk of range 2r. Most of existing works already rely on the assumption that if the communication range is at least twice the sensing range then full area coverage implies the covering set to be connected. Here, the resulting set could be connected if full coverage were provided. Meanwhile, results show less than 100% of area coverage even when the threshold is fixed at 0.0. [TG] "A Coverage-Preserving Node Scheduling Scheme for Large Wireless Sensor Networks", Tian and Georganas [JD] "A coverage preserving density control algorithm for wireless sensor networks", Jiang and Dou [CGSS] "Localized Sensor Area Coverage with low Communication Overhead", Carle, Gallais, Simplot-Ryl and Stojmenovic III. CONFIDENTIAL COMMENTS (IF ANY) to be withheld from the author(s): ------------------------------------ Comments given under THIS item are for the EDITORS ONLY (to be withheld from the authors).