#### DMCA

## Index Terms

### Citations

1565 |
Fundamentals of Statistical Signal Processing: Estimation Theory
- Kay
- 1993
(Show Context)
Citation Context ... well-known that when the likelihood function is a multivariate Gaussian pdf CN (m(θ),Σ) with the dependence on the parameters in the mean, then the Fisher information matrix J(θ) has (a, b) elements =-=[43]-=- Ja,b(θ) = 2Re {( ∂m(θ) ∂θa )H Σ−1 ∂m(θ) ∂θb } . In our case, we have Σ = N0I, m(θ) = Ξ(δξ)S∇(δµ)h, and the vector of parameters θ has elements θ1 = δξ, θ2 = δµ, θ2p+3 = Re{hp}, θ2p+4 = Im{hp}, p = 0,... |

424 |
Femtocell networks: a survey
- Chandrasekhar, Andrews, et al.
- 2008
(Show Context)
Citation Context ...y channel resource by eliminating multiuser interference via spatial precoding, using a very large number of antennas at each base station site [1], [2]. The latter pertains to the use of small cells =-=[3]-=-, such that multiple short-range low-power links can co-exist on the same time-frequency channel resource thanks to sufficient spatial separation. Distributed Multiuser MIMO (MUMIMO) unifies these two... |

385 | Robust frequency and timing synchronization for ofdm
- Schmidl, Cox
- 1997
(Show Context)
Citation Context ...ignals with negligible inter-carrier interference (ICI). This can be implemented by completely standard schemes used in current WLAN technology and forming a well-known and thoroughly studied subject =-=[9]-=-–[13]. Hence, such blocks need not be treated explicitly in this paper. In contrast, synchronization at the AP transmitter side plays a critical role in the distributed MU-MIMO architecture, since it ... |

319 | A technique for orthogonal frequency division multiplexing frequency offset correction - Moose - 1994 |

272 |
Noncooperative cellular wireless with unlimited numbers of base station antennas
- Marzetta
- 2010
(Show Context)
Citation Context ...fers to serving multiple users on the same time-frequency channel resource by eliminating multiuser interference via spatial precoding, using a very large number of antennas at each base station site =-=[1]-=-, [2]. The latter pertains to the use of small cells [3], such that multiple short-range low-power links can co-exist on the same time-frequency channel resource thanks to sufficient spatial separatio... |

239 |
for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks Specific Requirements Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless
- Standard
- 2006
(Show Context)
Citation Context ...libration) needed to enable such coherent DL MU4MIMO transmission. OFDM is assumed throughout this paper, since it is widely used in current WLAN (802.11a/g/n/ac) and cellular (LTE/802.16m) standards =-=[7]-=-. An UL-pilot/DL-precoded transmission cycle works as follows. At first, UL pilots are transmitted by the User Terminals (UTs). After receiving the UL pilots, each AP individually processes its observ... |

112 | Multiuser MIMO achievable rates with downlink training and channel state feedback
- Caire, Jindal, et al.
- 2010
(Show Context)
Citation Context ...data symbols to be sent to the Nu UTs, and G[m, ν] is the Nu×Na MU-MIMO precoding matrix for OFDM symbol m and subcarrier ν. In this work we consider linear Zero-Forcing Beamforming (ZFBF) [2], [28], =-=[33]-=- and conjugate beamforming [1], [2], [28], the details of which are given later on in this section. The two matrices Θ[m, ν] and Φ[m, ν] are diagonal of dimension Nu×Nu and Na×Na, respectively, with d... |

91 | A fast and accurate single frequency estimator. - Kay - 1989 |

72 | Achieving ‘massive MIMO’ spectral efficiency with a not-so-large number of antennas - Huh, Caire, et al. - 2012 |

69 | Distributed transmit beamforming: challenges and recent progress
- Mudumbai, Brown, et al.
- 2009
(Show Context)
Citation Context ...bration have been treated to some extent in the existing literature. The synchronization of multiple transmitters for multiple-input singleoutput (MISO) cooperative beamforming is considered in [18], =-=[19]-=-, and software-defined radio (SDR) implementations of such ideas are presented in [20]–[22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in ... |

66 |
Precision clock synchronization protocol for networked measurement and control system
- Standard
- 2004
(Show Context)
Citation Context ...speed from/to the CS, but not able to distribute a common clock (i.e., timing and phase information) to the APs, beyond the limitations of standard network synchronization protocols such as IEEE 1588 =-=[4]-=-. In order to achieve large spectral efficiencies through MU-MIMO downlink spatial precoding, channel state information at the transmitter (CSIT) is needed. Following the massive MIMO approach [1], [2... |

63 |
Complex-valued matrix differentiation: Techniques and key results
- Hjorungnes, Gesbert
(Show Context)
Citation Context ...roblem is given by Fcal(c, λ) = Jcal(c)− λ(‖c‖2 − 1). (27) where λ is the Lagrangian multiplier. Differentiating Fcal with respect to c∗i , treating ci and c ∗ i as if they were independent variables =-=[40]-=-, and then setting the partial derivatives to zero, we obtain ∂ ∂c∗i Fcal(c1, c2, . . . , cNa , λ) = ∑ j:(i,j)∈Fu ( ci|Yi→j |2 − cjY ∗i→jYj→i )− λci. (28) In matrix form, we obtain Ac = λc, where A is... |

58 | Coherent cooperative transmission from multiple adjacent antennas to a distant stationary antenna through AWGN channels
- Tu, Pottie
(Show Context)
Citation Context ...y calibration have been treated to some extent in the existing literature. The synchronization of multiple transmitters for multiple-input singleoutput (MISO) cooperative beamforming is considered in =-=[18]-=-, [19], and software-defined radio (SDR) implementations of such ideas are presented in [20]–[22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our ow... |

51 | Network MIMO with linear zeroforcing beamforming: Large system analysis, impact of channel estimation, and reduced-complexity scheduling
- Huh, Tulino, et al.
- 2012
(Show Context)
Citation Context ...work implementations and it is not widely treated in the literature (see the existing-results overview provided below). In fact, in most theoretical works on distributed MU-MIMO (see for example [2], =-=[14]-=-–[17]) perfect transmitter synchronization is assumed without specifying how this is achieved. As shown in Section II-A, uncompensated synchronization errors at the AP transmitter side cannot be undon... |

48 | Maximum-likelihood synchronization and channel estimation for the uplink of an
- Pun, Morelli, et al.
- 2006
(Show Context)
Citation Context ...ls with negligible inter-carrier interference (ICI). This can be implemented by completely standard schemes used in current WLAN technology and forming a well-known and thoroughly studied subject [9]–=-=[13]-=-. Hence, such blocks need not be treated explicitly in this paper. In contrast, synchronization at the AP transmitter side plays a critical role in the distributed MU-MIMO architecture, since it needs... |

47 | Argos: Practical many-antenna base stations.
- Shepard, Yu, et al.
- 2012
(Show Context)
Citation Context ...e the presence or collaboration of the UTs, which may be legacy devices not necessarily implementing the protocol. A novel TDD reciprocity calibration method, referred to as “Argos”, was presented in =-=[28]-=- as part of an SDR implementation of a TDD reciprocity-based massive MIMO base station. This method enables calibration by exploiting two-way signaling that involves only base station antennas, exchan... |

39 | Time and frequency synchronization for OFDM using PN-sequence preambles. - Tufvesson, Edfors, et al. - 1999 |

30 | JMB: scaling wireless capacity with user demands.
- Rahul, Kumar, et al.
- 2012
(Show Context)
Citation Context ... software-defined radio (SDR) implementations of such ideas are presented in [20]–[22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in [23]–=-=[25]-=-, where the feasibility of overthe-air synchronization with enough accuracy to guarantee near-ideal multiuser interference suppression is demonstrated. These works are based on a master-slave protocol... |

29 | The L(h, k)-labelling problem: A survey and annotated bibliography
- Calamoneri
- 2006
(Show Context)
Citation Context ... We require that each anchor node is able to receive the pilot bursts from its neighboring anchor nodes without significant co-pilot interference. This is possible by finding an L(1, 1)-labeling (see =-=[35]-=- and references therein) of the subgraph (A, E(A)), and associating pilot bursts to the labeling colors. An L(1, 1)-labeling of a graph is a coloring scheme for which all neighbors of any node i ∈ A h... |

22 | Cellular vs network MIMO: A comparison including channel state information overhead - Ramprashad, Caire - 2009 |

20 | Lowcomplex frame synchronization in OFDM systems - Beek, Sandell, et al. |

18 | Multiuser MISO transmitter optimization for intercell interference mitigation
- Huh, Papadopoulos, et al.
- 2010
(Show Context)
Citation Context .... 6. 18Backing off the transmit power in order to meet the per-AP power constraint is suboptimal. The optimal MU-MIMO zeroforcing precoding with per-antenna power constraint is discussed in detail in =-=[42]-=-, and its optimization requires non-uniform power allocation per DL data stream and can be obtained using the theory of generalized inverses and convex relaxation. Here, we chose to use a more practic... |

17 | On Base Station Cooperation Schemes for Downlink Network MIMO under a Constrained Backhaul,
- Marsch, Fettweis
- 2008
(Show Context)
Citation Context ...implementations and it is not widely treated in the literature (see the existing-results overview provided below). In fact, in most theoretical works on distributed MU-MIMO (see for example [2], [14]–=-=[17]-=-) perfect transmitter synchronization is assumed without specifying how this is achieved. As shown in Section II-A, uncompensated synchronization errors at the AP transmitter side cannot be undone at ... |

17 |
Achieving high data rates in distributed MIMO systems.
- Balan, Rogalin, et al.
- 2012
(Show Context)
Citation Context ..., and software-defined radio (SDR) implementations of such ideas are presented in [20]–[22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in =-=[23]-=-–[25], where the feasibility of overthe-air synchronization with enough accuracy to guarantee near-ideal multiuser interference suppression is demonstrated. These works are based on a master-slave pro... |

13 |
Relative channel reciprocity calibration
- Kaltenberger, Haiyong, et al.
- 2010
(Show Context)
Citation Context ...refore, reciprocity for such systems typically does not hold. 3the transmitter and receiver hardware are not, and introduce an unknown amplitude scaling and phase shift between the UL and DL channels =-=[6]-=-. Furthermore, in order to have all the remote APs behave as a single distributed multiple antenna system, the APs must maintain relative timing and phase synchronism throughout the duration of a DL p... |

12 | Fully wireless implementation of distributed beamforming on a software-defined radio platform,”
- Rahman, Baidoo-Williams, et al.
- 2012
(Show Context)
Citation Context ...on of multiple transmitters for multiple-input singleoutput (MISO) cooperative beamforming is considered in [18], [19], and software-defined radio (SDR) implementations of such ideas are presented in =-=[20]-=-–[22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in [23]–[25], where the feasibility of overthe-air synchronization with enough accuracy t... |

10 | Demonstrating distributed transmit beamforming with softwaredefined radios - Quitin, Madhow, et al. - 2012 |

10 |
Threshold behavior of the maximum likelihood estimator of frequency
- Quinn, Kootsookos
- 1994
(Show Context)
Citation Context ...iently large” means above some design threshold determined by the system designer. 7the corresponding Cramer-Rao Bound (CRB) as a good approximation of the estimation MSE achievable in practice [29], =-=[30]-=-. The rest of this paper is organized as follows. Section II presents a simplified but sufficiently accurate model for OFDM in the presence of timing, sampling frequency and carrier frequency offsets,... |

9 | Network MIMO with reduced backhaul requirements by MAC coordination,” in - Boccardi, Huang, et al. - 2008 |

8 |
Distributed beamforming with software-defined radios: frequency synchronization and digital feedback
- Quitin, Mahboob, et al.
- 2012
(Show Context)
Citation Context ... multiple transmitters for multiple-input singleoutput (MISO) cooperative beamforming is considered in [18], [19], and software-defined radio (SDR) implementations of such ideas are presented in [20]–=-=[22]-=-. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in [23]–[25], where the feasibility of overthe-air synchronization with enough accuracy to gua... |

7 |
Algorithms for connected set cover problem and fault-tolerant connected set cover problem
- Zhang, Gao, et al.
- 2009
(Show Context)
Citation Context ...dices, if (i, j) ∈ E then also (j, i) ∈ E . Without loss of generality, we assume 15 that the graph (T , E) is connected.12 For the synchronization protocol, we define A ⊆ T to form a connected cover =-=[34]-=-, i.e., the subgraph formed by the APs i ∈ A and their associated edges E(A) = {(i, j) : i, j ∈ A} is connected and any other AP i′ /∈ A has at least one neighbor in A. The APs in A are referred to as... |

6 |
A distributed consensus approach to synchronization of rf signals,”
- Rahman, Dasgupta, et al.
- 2012
(Show Context)
Citation Context ... with sufficiently large power and thus limiting the size and topology of the network. Extensions to networks of arbitrary size and topology based on distributed consensus protocols are considered in =-=[26]-=-, [27]. The slow rate of convergence, however, makes such schemes impractical for large networks. 3 TDD reciprocity was considered in [6], presenting a calibration technique based on exchanging pilot ... |

3 | Molisch, “Hardware-impairment compensation for enabling distributed large-scale
- Rogalin, Bursalioglu, et al.
(Show Context)
Citation Context ...AP are driven by a common clock and therefore need only to be calibrated but not mutually synchronized. Hierarchical calibration in multiple steps is naturally suited to this purpose, as evidenced in =-=[8]-=-, [38]. It is also interesting to notice that the proposed synchronization scheme calculates the timing and frequency correction factors relative to some particular anchor AP (denoted by AP 1 in Secti... |

3 |
Ultra-wide bandwidth timing networks
- Niranjayan, Molisch
(Show Context)
Citation Context ...sufficiently large power and thus limiting the size and topology of the network. Extensions to networks of arbitrary size and topology based on distributed consensus protocols are considered in [26], =-=[27]-=-. The slow rate of convergence, however, makes such schemes impractical for large networks. 3 TDD reciprocity was considered in [6], presenting a calibration technique based on exchanging pilot signal... |

2 |
TGac Channel Model Addendum
- 11-090308r12
- 2010
(Show Context)
Citation Context ...nce time for typical wireless local area networks with nomadic users may span ∼ 0.1s to 1s or more. In fact, 800 msec is commonly used as the simulation assumption for 801.11ac IEEE standard for WLAN =-=[5]-=-. In WARP software-radio based experiments, we observed the coherence time to be about 1 second. In contrast, Frequency Division Duplexing schemes have the UL and the DL separated by tens of MHz, well... |

2 | Enabling Distributed Multiuser MIMO With Full Spatial Multiplexing - “AirSync |

2 |
Intercarrier Interference in OFDM: A General Model for Transmissions in Mobile Environments with Imperfect Synchronization
- Garcı́a, Oberli
- 2009
(Show Context)
Citation Context ...r (ADC), anti-aliasing filter, etc.). Since the CFO between node i and node j is small with respect to the signal bandwidth, the complex baseband signal after demodulation can be written as (see also =-=[31]-=-) ỹi→j(t) = (∑ n N−1∑ k=−L x̃i[n, k]gi→j (t− (τi − τj)− (n(N + L) + k)Ts,i) ) × exp(j2pi(f0,i − f0,j)t), (3) where we define 5 gi→j(t) = (Πi ⊗ hi→j)(t), with Πi(t) = Π(t/Ts,i). The ADC at receiver j ... |

2 |
MU-MIMO in LTE: Performance and the challenges for future enhancement,” ICC’2012
- Ramprashad, Benjebbour
- 2012
(Show Context)
Citation Context ...by the frame structure of Fig. 3. The calibration slot is formed by pilot symbols arranged on the time-frequency plane induced by OFDM, as commonly 22 implemented for channel estimation purposes [7], =-=[36]-=-, [37]. Since the non-reciprocal elements of the channel (due to the modulation/demodulation hardware) are smooth over the signal bandwidth both in amplitude and in phase, the calibration pilots can b... |

2 |
Towards Realizing Scalable Large-Scale MIMO with Non-Colocated Arrays
- Papadopoulos
(Show Context)
Citation Context ...iting the correlation between the calibration coefficients at different subcarriers can be exploited to improve estimation accuracy. More details on efficient calibration pilot design are provided in =-=[38]-=-, [39] and go beyond the scope of this work. Here, for the sake of clarity, we focus on a single subcarrier and drop the subcarrier index ν from the notation. In order to motivate the need for TDD rec... |

2 |
Efficient Hierarchical Reciprocity Calibration of Large TDD Networks
- Papadopoulos, Bursalioglu
- 2013
(Show Context)
Citation Context ...the correlation between the calibration coefficients at different subcarriers can be exploited to improve estimation accuracy. More details on efficient calibration pilot design are provided in [38], =-=[39]-=- and go beyond the scope of this work. Here, for the sake of clarity, we focus on a single subcarrier and drop the subcarrier index ν from the notation. In order to motivate the need for TDD reciproci... |