Wonjong Rhee's research while affiliated with ASSIA Inc. and other places
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Publications (22)
With the latest technology of vectoring, DSL data rates in the order of 100Mbps have become a reality that is under field deployment. The key is to cancel crosstalk from other lines, which is also known as multiuser MIMO cancellation for wireless communications. During the DSL system upgrade phase of field deployment, mix of legacy and vectoring-en...
Methods, apparatus and computer program products allow a user of DSL or the like to implement user preferences to the extent feasible in light of operational limits and conditions. In some embodiments, an operational profile is imposed on the user. User preference data is evaluated to determine the extent to which one or more user preferences can b...
The severe interference from neighbor copper lines, commonly known as crosstalk, is a well-known limitation that can reduce the upstream rate of a victim user by 50% or more in dense VDSL (Very high bit-rate Digital Subscriber Lines) deployment. This problem has been partially addressed by the use of UPBO (Upstream Power BackOff). UPBO blindly cont...
The severe interference from neighbor copper lines, commonly known as crosstalk, is a well-known limitation that can cause 50% or larger reduction in the upstream rates of dense VDSL (Very high bit-rate Digital Subscriber Lines) deployments. To handle this problem, UPBO (Upstream Power BackOff) has been studied in literature, and subsequently stand...
This paper investigates the benefits of Dynamic Spectrum Management (DSM) in terms of reducing the power consumption and improving
the data rates in digital-subscriber-line (DSL) networks. The proposed techniques at the three different DSM levels simultaneously
also provide a significant improvement in the stability of DSLs. The proposed DSM method...
Power-saving benefits of Dynamic Spectrum Management (DSM) result from its increased robustness to channel and noise changes, as in this paper. A proposed intermittent noise model enables evaluation of the performance of DSM algorithms. Polite Level-1 DSM algorithm consumes much less power than non-polite DSL management algorithms in the presence o...
This letter investigates the structure of the optimal spatial multiplex scheme in a multiuser multiantenna wireless fading environment. Based on a sum-capacity criterion, this letter shows that the optimal transmission strategy in an uplink or downlink channel with n antennas at the base-station involves more than n users at the same time. In parti...
Multiple-input multiple-output (MIMO) flat-fading channels with channel state information available at the receiver and channel state distribution available at the transmitter are considered. The ergodic capacity-achieving covariance matrix (ECACM) under an average input power constraint is shown to be not unique in general, and three sufficient co...
In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaussian broadcast channel (BC). It was recently found that dirty-paper coding is capacity achieving for this channel. In order to achieve capacity, the optimal transmission policy (i.e., the optimal transmit covariance structure) given the channel conditio...
This paper proposes an efficient numerical algorithm to compute the optimal input distribution that maximizes the sum capacity of a Gaussian multiple-access channel with vector inputs and a vector output. The numerical algorithm has an iterative water-filling interpretation. The algorithm converges from any starting point, and it reaches within 1/2...
This paper considers the optimal uplink transmission strategy that achieves the sum-capacity in a multiuser multi-antenna wireless system. Assuming an independent identically distributed block-fading model with transmitter channel side information, beamforming for each remote user is shown to be necessary for achieving sum-capacity when there is a...
This paper characterizes the capacity region of a Gaussian multiple access channel with vector inputs and a vector output with or without intersymbol interference. The problem of finding the optimal input distribution is shown to be a convex programming problem, and an efficient numerical algorithm is developed to evaluate the optimal transmit spec...
The advantages of multiuser communication, where many users are allowed to simultaneously transmit or receive in a common bandwidth, are considered for multiple-antenna systems in a high signal-to-noise ratio (SNR) regime. Assuming channel state information at receiver (CSIR) to be available, the ergodic capacity is characterized for both unbiased...
An efficient algorithm for computing the sum capacity of vector broadcast channel is obtained in this paper. This algorithm utilizes the duality between broadcast and multiple access channels and the Kuhn-Tucker conditions of sum power multiple access channel.
Recent research has shown that the capacity of a multiple antenna system grows linearly with increasing number of antennas for rich-scattering environments. However, this is not true for wireless channels with small number of independent paths. To overcome this problem, this paper investigates the possibility of exploiting multiuser dimension with...
This paper characterizes the optimal power control method for maximum sum capacity in a multiple access fading channel with multiple transmitter and receiver antennas when perfect channel side information is available at both the transmitters and the receiver. The profound benefit of multi-antenna diversity is demonstrated by a dimension counting a...
In this paper, the ergodic capacity region of multi-antenna multiple-access channels is derived, and the quantitative capacity gains of multiuser communication systems are investigated. In many multi-antenna communication scenarios, the ergodic capacity of multiuser systems, where many users are allowed to simultaneously transmit or receive in a co...
In this paper, transmit schemes for multi-antenna Gaussian
multiple access channels are considered. For the case of a large number
of users, a short term power constraint, and slowly fading channels,
asymptotic optimality of beamforming is shown under the sum rate
maximization criterion. This is an interesting result because the
optimal transmit sc...
This paper characterizes the optimal power control method for
maximum sum capacity in a multiple access fading channel with multiple
transmitter and receiver antennas when perfect channel side information
is available at both the transmitters and the receiver. The profound
benefit of multi-antenna diversity is demonstrated by a dimension
counting a...
This paper investigates the problem of dynamic multiuser
subchannel allocation in the downlink of OFDM systems. The assumptions
are that the channel model is quasi-static and that the base station has
perfect channel information. In traditional TDMA or FDMA systems,
resource allocation for each user is non-adaptively fixed, and the
water-filling po...
Previous research has shown that the capacity of a multiple
antenna system grows linearly with increasing number of antennas for
rich-scattering environments. However, this is not true for wireless
channels with a small number of independent paths. To overcome this
problem, this paper investigates the possibility of exploiting the
multiuser dimensi...
The use of band preference in DSL systems with dynamic spectrum management (DSM) is investigated. Specifically, band preference is a DSM center's allocation of approxi-mate PSD masks for subsequent use in the commonly en-countered fixed-margin or "iterative" water-filling DMT DSL systems is found to improve data rates when DSL line lengths differ....
Citations
... That being the case, the high-speed interconnect needs to connect to the DSLAM (DSL Access Multiplexer) at the user's exchange. There is ongoing research as new technologies emerge on adapting DSLAMs [29] so factoring in one more relatively simple service should not be a problem. At the point the service enters the DSLAM, it requires the bandwidth of a single movie and the content can be wrapped in standard IP packets. ...
Reference: Video on demand in a high bandwidth world
... This process of handling the transmit PSDs is known as upstream power back off (UPBO). There exist several methods by which UPBO process is performed [1][2][3][6][7][8][9]. ...
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... The purpose of collecting data regarding customer line behavior can be simply to report and analyze or more substantially to conduct proactive service improvement activities. An example is activities performed by dynamic spectrum management systems (DSMs) 39,40 in the case of digital subscriber line (DSL) technologies. ...
... As well, in practice, the number of active users changes constantly and therefore in order to make effective use of the spectrum, in order to maximize the achievable bit-rate it is essential to dynamically allocate transmit PSDs. Therefore, this led to the introduction of Dynamic Spectrum Management (DSM) [3,4]. ...
... Iterative water-filling (IWF) is probably the most widely studied approach for allocating spectral resources in DSCNs. Among the most relevant contributions regarding the IWF , we highlight those in [79,[82][83][84][85][86][87][88]. Even though IWF can be considered a special case of a learning algorithm known as best-response dynamics (BRD), it considered as originated in the field of information theory [88] and its applications were first studied in digital subscriber lines' power control. ...
Reference: Decisional process for ad hoc networks.
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... Therefore, the performance in terms of data rate of far end users is more degraded compared to that of near end users as far end users suffer from more FEXT compared to near end users. This effect is known as 'Near-Far' problem [1][2][3][4][5]. ...
... Together with an almost linear relation between line-driver power consumption and transmit power it is clear that reducing transmit power will reduce the overall power and therefore energy consumption. Therefore it is expected that many of the dynamic spectrum management (DSM) methods will help to reduce power consumption as they are designed to reduce interference among the users [6]. Recently it was shown that there is a benefit from optimizing directly for energy efficiency, using the energy-efficient spectrum balancing (EESB) algorithm [7], instead of getting an indirect power reduction through standard DSM methods, like optimal spectrum balancing (OSB) [5], which in fact try to maximize rate. ...
... A N ANALYTICAL evaluation of the covariance matrix of correlated complex-valued Nakagami-m fading channels is highly important [1], particularly for principal component combining (PCC) [2], simulator development [3]- [5], and throughput increment and channel estimations for multi-inputmulti-output (MIMO) systems [6]- [8]. In [2], eigenvalue decomposition (EVD) was applied to the covariance matrix of correlated complex-valued Nakagami-m fading channels, and the covariance matrix was assumed to be known a priori. ...
... The proposed IM method in combination with widelystudied Water Filling (WF) [50] show a significant gain in spectral efficiency while using a similar computing time as the reference Equal Power (EP) solution (see Fig. 9.) ...
... 1) Optimization of the Power Allocation p under Given Θ: When Θ is given, the original problem is reduced to a power allocation problem considering interference from other channels under a total power constraint. The iterative water-filling algorithm, with computational complexity O(K) per iteration, can progressively increase the sum rate [12]. Furthermore, we introduce a weighted summation step by superimposing the updated solution with the previous iteration's result to enhance the stability of the algorithm. ...
