======= Review 1 =======
> *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research.
Good (4)
> *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the
analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour.
Valid work but limited contribution. (3)
> *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper.
Some interesting ideas and results on a subject well investigated. (3)
> *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references.
Well written. (4)
> *** Strong aspects: Comments to the author: what are the strong aspects of the paper?
This paper analyzes the performance gain by introducing MIMO relay in a theoretical way. The analysis takes into account the overhead due to pilot and channel feedback as well as the performance loss due to finite feedback, which makes the results realistic.
The discussion on the numerical results is well-formulated.
> *** Weak aspects: Comments to the author: what are the weak aspects of the paper?
The analysis in this paper basically uses the results from previous publications, and so the contribution in terms of theoretical analysis is not so significant.
In the section of numerical results, while the other observations are expected and/or known in the varied previous works, the observation concerning the optimal feedback bits is quite interesting because it is said to be somehow against the conclusions from the previous publications.
However, firstly, this interesting observation is only discussed in one short paragraph and the reader would be much more interested to see more discussion on this aspect. Secondly, the observation is about the relationship between the optimal feedback bits and the SNR, but it is the relationship between the optimal feedback bits and the duration of super-slot that is depicted in Fig. 6: the figure has to be mistakenly presented. Therefore, it still remains to how the results is against the conclusions made in the previous literatures, as stated in page 5, left column, last paragraph.
The paper is well-written but there are a number of errors in equations and figures which need to be corrected. Some of them are confusing, especially to the readers who are not familiar with the topic. Please refer to the section ˇ°recommended changesˇ± for details.
> *** Recommended changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted.
Page 3, left column, equation (3)
- the superscript * seems to represent ˇ°complex transpose operationˇ± rather than ˇ°complex conjugate operationˇ± as stated.
- the term [ˇ¦]^_{n,n} is supposed to be [ˇ¦]_{n,n} without inverse, because inside the square brackets is the pseudo-inverse of the channel matrix H.
- the term on the top of the sum symbol is supposed to be the number of data streams and should therefore be the minimum between N_br (the number of antennas at the BS) and N_rn (the number of antennas at the relay).
- the term SNR_br/K is apparently an error, since K (the number of users) would never have any impact on R_{br, i}, i.e. the throughput of BS-relay link. It is more reasonable for the term to become SNR_br/N_rn with N_rn being the number of receiving antennas. In this case, the receiving SNR, denoted by SNR_br, is assumed to be defined as the total power of the signal received on all N_rn receiving antennas divided by the noise power received on each receiving antenna, which should have been defined in the context.
Page 3, right column, first lines 1-2:
Either \hat_j or G_j is not correct, because the current expressions suggest that \hat_j and its pseudo inverse G_j are of the same dimension, i.e. N_bs x K. Generally, the downlink transmission is expressed as y = Hx + n, and so the downlink channel matrix \hat_j is a N_bs x K ? dimensional matrix, which follows that \hat_j should be extended as [h_*, ˇ¦, h_*]*.
Indeed, it would be quite helpful for the reader if the dimension of the channel matrix, both H_i and \hat_j, is explicitly provided.
Page 3, right column, Lemma 1:
- N_bs on the left side of equation (5) is supposed to be N_rn, since the throughput for the relay-user link should have nothing to do with the number of antennas at the BS, i.e. N_bs.
- N_ru in equation (6) should be N_rn.
- According to equation (5), it seems that SNR_ru in equation (6) should rather be replaced by SNR_ru / N_rn.
Page 5, left column, last paragraph related to Fig. 6: Fig. 6 illustrates how the optimal number of feedback bits B* changes with BS-relay link super-slot given a constant SNR_br of 30 dB. However, the corresponding discussion on Fig. 6 is about the relationship between the optimal number of feedback bits B* and the SNR value (see last paragraph). It seems that a wrong figure is mistakenly presented, which has to be amended.
Page 4, left column, last 4th line: the term ˇ°mini-slotˇ± is used in the explanation for Fig. 4, while the sum throughput is depicted with respect to super-slot in Fig. 4. Although the super-slot is composed of multiple mini-slot and thus small super-slot also suggests small mini-slot, it is still better to e.g. presenting the throughout with respect to mini-slot in Fig. 4 so as to be fully consistent with the explanations.
Page 3, left column, line 8: log(1+N_SNR_) should be log(1+N_SNR) according to equation (2).
Page 3, left column, line 5: the word ˇ°inˇ± in the expression ˇ°ˇ¦ where there in pilot overhead only, ˇ¦ˇ± should be ˇ°isˇ±.
======= TPC Review 2 =======
> *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research.
Excellent (5)
> *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the
analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour.
Solid work of notable importance (4)
> *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper.
Significant original work and novel results. (4)
> *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references.
Well written. (4)
> *** Strong Aspects: Comments to the author: what are the strong aspects of the paper?
The idea of relays mounted on vehicles to support user's mobility is interesting although somewhat obvious. The paper makes important observations about overheads in multiuser MIMO systems supporting users' mobility.
> *** Weak Aspects: Comments to the author: what are the weak aspects of the paper?
I did not find any particularly weak aspects. The paper may consider mobility i.e. what speeds would be supported by the proposed mobile relay.
> *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted.
I have no recommended changes.
======= TPC Review 3 =======
> *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research.
Good (4)
> *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the
analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour.
Valid work but limited contribution (3)
> *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper.
Significant original work and novel results. (4)
> *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references.
Well written. (4)
> *** Strong Aspects: Comments to the author: what are the strong aspects of the paper?
This paper does consider a wireless architecture worthy of investigation addressing the delivery of boardband services
> *** Weak Aspects: Comments to the author: what are the weak aspects of the paper?
How do the results relate to competing technologies such as Femto Cells? What channel models were used.
> *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted.
Clarification on the channel models used
======= TPC Review 4 =======
> *** Relevance and timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research.
Good (4)
> *** Technical content and scientific rigour: Rate the technical content of the paper (e.g.: completeness of the
analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour.
Valid work but limited contribution (3)
> *** Novelty and originality: Rate the novelty and originality of the ideas or results presented in the paper.
Some interesting ideas and results on a subject well investigated. (3)
> *** Quality of presentation: Rate the paper organization, the clearness of text and figures, the completeness and accuracy of references.
Readable, but revision is needed in some parts. (3)
> *** Strong Aspects: Comments to the author: what are the strong aspects of the paper?
The main advantage of the proposed system is the improvement of the throughput due to the use of the relay.
> *** Weak Aspects: Comments to the author: what are the weak aspects of the paper?
1. The paper is hard to follow in some places.
2. The motivation of the work is not very strong. The argument that the end user size does not allow the end user to have enough number of antennas with enough spacing to achieve diversity is not well supported by numerical results.
3. The new system has very high complexity due to the introduction of the relay.
> *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted.
1. The authers should avoid saying "our proposed", it is better to say "the proposed".
2. A more clear defintion for the baseline system should be given.