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This paper presents an orthogonal frequency division multiple access (OFDMA) channel estimation technique that jointly considers the effects of coarse timing error and multipath propagation. Many conventional approaches only consider an optimistic scenario where timing synchronization is perfect and each of the channel delays is an integer number o...
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... Cable television (CATV) networks are governed by a set of DOCSIS standards that place hard limits on bandwidth and data rates. The latest version of the DOCSIS standard, DOCSIS 3.1 was released in October 2013. DOCSIS 3.1 increases the bandwidth and data throughput available in CATV networks by up to 10 Gbps downstream and 1 Gbps upstream. Fig. 1 shows a simplified structure of a cable network. There are two main components in the network: a cable modem (CM), which is located at the customer premises, and a cable modem termination system (CMTS), located at the cable company's headend. The CMTS is responsible for managing a large number of cable modems residing in subscribers' ...
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... . Therefore, the timing variance of the initial ICE algorithm would asymptotically approach U −2 /12, which are the four horizontal lines in Fig. 9 tagged with U = 1, U = 4, U = 32 and U = 2048. As such, the interpolation method introduced in Section IV-B is very important as it provides excellent timing estimates for a small computational cost. Fig. 10 illustrates the performance for a 6 echo scenario (L=7), where the 6 echoes have strengths and delays as specified in Table. I. ǫ 1 is constrained to be greater or equal to 1 and L = L = 7. The simulation was run for two different skipping factors: K = 1, i.e. no sub-carrier skipping, and K = 4 which limits the number of pilot ...
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... shown Fig. 10, the performance for K = 4 is about 6 dB worse than for K = 1. This makes sense since the noise power σ 2 ρ = σ 2 w M is inversely proportional to M , so it increases by 6 dB when the number of pilot sub-carriers is reduced from 1900 to 475. Therefore, experimental evidence suggests that the performance of the ICE technique scales well ...
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... about 6 dB worse than for K = 1. This makes sense since the noise power σ 2 ρ = σ 2 w M is inversely proportional to M , so it increases by 6 dB when the number of pilot sub-carriers is reduced from 1900 to 475. Therefore, experimental evidence suggests that the performance of the ICE technique scales well with the number of pilot sub-carriers. Fig. 11 shows the MSE performance when the estimated number of channel paths, L, differs from the true number of paths, L. The simulation parameters are the same as in Fig. 10 for the 7 paths channel described in Table I. The skipping factor is K = 1 and the SNR is varied from 10 to 40 dB. When SNR = 10 dB, the best performance is achieved ...
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... sub-carriers is reduced from 1900 to 475. Therefore, experimental evidence suggests that the performance of the ICE technique scales well with the number of pilot sub-carriers. Fig. 11 shows the MSE performance when the estimated number of channel paths, L, differs from the true number of paths, L. The simulation parameters are the same as in Fig. 10 for the 7 paths channel described in Table I. The skipping factor is K = 1 and the SNR is varied from 10 to 40 dB. When SNR = 10 dB, the best performance is achieved when L = 4. This is because the power of the 4 th , 5 th and 6 th echoes are close to or less than the noise power, σ 2 ρ , and thus can not be detected properly. A ...
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... the raw bit error rate performance (i.e., without channel coding) of the proposed estimator under the 6-echo channel model is shown in Fig. 12. The parameters for the 4 designs considered are shown in the figure. The other simulation parameters are N = 4096, M = 3800 and U = 2. The modulation orders for data sub-carriers are 1024-QAM and 4096-QAM, which gives the highest throughput that DOCSIS 3.1 can achieve. Design 1 has the worst performance since such a large skipping ...
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... A related problem is that of delay estimation in a general multiple access system, such as orthogonal frequency division multiple access (OFDMA). One recent work studies the problem of delay estimation in OFDMA uplink channels specified by the DOCSIS 3.1 standard, 16 in which an iterative method centering on peak detection of the inverse fast Fourier transform of a received pilot sequence. Another paper utilizes a compressed sensing technique 17 similar to the technique employed in our work. ...
Despite being the subject of a growing body of research, nonorthogonal multiple access has failed to garner sufficient support to be included in modern standards. One of the more promising approaches to nonorthogonal multiple access is sparse code multiple access, which seeks to utilize nonorthogonal, sparse spreading codes to share bandwidth among users more efficiently than traditional orthogonal methods. Nearly all of the studies regarding sparse code multiple access assume synchronization at the receiver, which may not always be a practical assumption. In this work, we aim to bring this promising technology closer to a practical realization by dropping the assumption of synchronization. We therefore propose a compressed sensing‐based delay estimation technique developed specifically for an uplink sparse code multiple access system. The proposed technique can be used with nearly all of the numerous decoding algorithms proposed in the existing literature, including the popular message passing approach. Furthermore, we derive a theoretical bound regarding the recovery performance of the proposed technique and use simulations to demonstrate its viability in a practical uplink system.
... A related problem is that of delay estimation in a general multiple access system, such as orthogonal frequency division multiple access (OFDMA). One recent work studies the problem of delay estimation in OFDMA uplink channels specified by the DOCSIS 3.1 standard [17], in which an iterative method centering on peak detection of the inverse fast Fourier transform of a received pilot sequence. Another paper utilizes a compressed sensing technique [18] similar to the technique employed in our work. ...
Despite being the subject of a growing body of research, non-orthogonal multiple access has failed to garner sufficient support to be included in modern standards. One of the more promising approaches to non-orthogonal multiple access is sparse code multiple access, which seeks to utilize non-orthogonal, sparse spreading codes to share bandwidth among users more efficiently than traditional orthogonal methods. Nearly all of the studies regarding sparse code multiple access assume synchronization at the receiver, which may not always be a practical assumption. In this work, we aim to bring this promising technology closer to a practical realization by dropping the assumption of synchronization. We therefore propose a compressed sensing-based delay estimation technique developed specifically for an uplink sparse code multiple access system. The proposed technique can be used with nearly all of the numerous decoding algorithms proposed in the existing literature, including the popular message passing approach. Furthermore, we derive a theoretical bound regarding the recovery performance of the proposed technique, and use simulations to demonstrate its viability in a practical uplink system.
... By doing so, there will be N ISI − D fewer samples contributing ISI from the previous OFDM symbol, but there will be D samples of ISI contributed from the next OFDM symbol. In particular, (17) can be re-written as in equation (19). ...
... This is markedly different from normal OFDM systems where information about fractional sample timing is not important as long as the start of the DFT processing window is placed within the CP. A practical method for estimating the timing error can be found in [19]. ...
... To demonstrate the robustness of the proposed scheme the modulation type at each sub-carrier is increased to 16384-QAM, which corresponds to the highest throughput that DOCSIS 3.1 can achieve (although this mode is optional and not generally used in current systems). Moreover, rather than using the perfect channel parameters as in the above simulations, an iterative channel estimator (ICE) [19] is employed to obtain estimates of the channel parameters, as would be done in practice. The ICE technique is selected since it can estimate exact channel path gains and delays, which is required for the TEQ, rather than just frequency response as is the case with most other methods in the literature. ...
The current version of the data over cable service interface specification (DOCSIS), which is DOCSIS 3.1, is markedly different from previous versions in that orthogonal frequency-division multiplexing (OFDM) is used together with high-density QAM constellations (up to 4096-QAM) in both the downstream and upstream directions to facilitate high data rates. This is in a sharp contrast with the single-carrier modulation techniques used in prior versions of DOCSIS. Despite many advantages, a drawback of OFDM is the insertion of a cyclic prefix (CP) at the beginning of each transmitted OFDM symbol to mitigate inter-symbol interference (ISI). The CP, which is configurable, but can be as large as 25% of the symbol time for DOCSIS 3.1 downstream transmission, does not carry useful data and therefore reduces the overall transmission throughput. In general, not only the channel but also the transceivers' digital filters determine the ISI and therefore the length of the CP. In this paper, the aspects that determine the CP length are thoroughly addressed. A novel technique to eliminate the CP is introduced and analyzed. It is demonstrated that the CP can be completely removed with a negligible effect on the transmission performance using this technique. Moreover, the proposed technique requires only a modest amount of hardware, making it a promising candidate to be included in the a future version of DOCSIS.
... The recent DOCSIS 3.1 version supports both upstream and downstream data peak throughputs on the order of Gbps [92]. DOCSIS 3.1 includes Orthogonal Frequency Division Multiplexing (OFDM) for the physical layer modulation over the broadband spectrum to achieve high spectral efficiency [93]- [95]. DOCSIS 3.1 also incorporates high levels of QAM modulation (up to 16K), Low Density Parity Check (LDPC) Forward Error Correction (FEC), and a wide spectrum of 1.2 GHz in the downstream and 204 MHz in the upstream [93]. ...
In orthogonal frequency-division multiple access (OFDMA), carrier frequency offset (CFO) destroys the orthogonality between subcarriers due to Doppler effect of the channel and also causes inter-carrier interference (ICI) as well as multiple access interference (MAI). In this paper, CFO tracking algorithm for OFDMA system is presented to overcome the effect of ICI as well as MAI. The proposed algorithm employs normalized least-mean-square (NLMS) algorithm which tracks the residual carrier frequency offset in OFDMA system. The proposed NLMS-based tracking algorithm uses average of all residual carrier frequency offset (RCFO) for improving the mean square error (MSE) performance. The proposed NLMS-based frequency tracking along with frequency offset compensator improves the error performance by reducing the effect of ICI and MAI. Simulation results indicate that the proposed algorithm achieves better tracking performance in the presence of frequency offset. From the results, it is observed that the MSE of the proposed estimator is improved about 3.8 dB at SNR = 20 dB with the frequency offset.
This paper introduces a self-interference cancellation (SIC) technique for data over cable service interface specification (DOCSIS) 3.1 uplink system with full duplex. At DOCSIS 3.1 uplink environment with full duplex, cable modems (CMs) transmit their request information (upstream) to CM termination system (CMTS), and CMTS transmits its broadcasting data (downstream) through the same frequency band at the same time. Therefore, the upstream becomes a signal of interest (SoI), and consequently the high-power feedback downstream causes self-interference (SI) signal against SoI. However, under the practical DOCSIS 3.1 uplink environment, achieving time and frequency synchronization between upstream and downstream is a challenging problem and additional signal processing technique should be applied. Therefore, in order to improve the processing efficiency and to reflect practical communication environment, the time-domain SIC technique, which does not require any synchronization between upstream and downstream is proposed. Furthermore, since the proposed scheme can consider various practical signal processing aspects, such as multi-path fading channel estimation and nonlinear element estimation of SI signal, it can be efficiently applied for the practical DOCSIS 3.1 uplink system. Test results indicate that the uplink system with 1024QAM (mandatory maximum constellation) can be operated in the case that there is SI estimation interval with two OFDM symbols.
