Robert Baldemair

Ultra-dense networks in millimeter-wave frequencies

Demands for very high system capacity and end-user data rates of the order of 10 Gb/s can be met in localized environments by Ultra-Dense Networks (UDN), characterized as networks with very short inter-site distances capable of ensuring low interference levels during communications. UDNs are expected to operate in the millimeter-wave band, where wide bandwidth signals needed for such high data rates can be designed, and will rely on high-gain beamforming to mitigate path loss and ensure low interference. The dense deployment of infrastructure nodes will make traditional wire-based backhaul provisioning challenging. Wireless self-backhauling over multiple hops is proposed to enhance flexibility in deployment. A description of the architecture and a concept based on separation of mobility, radio resource coordination among multiple nodes, and data plane handling, as well as on integration with wide-area networks, is introduced. A simulation of a multi-node office environment is used to demonstrate the performance of wireless self-backhauling at various loads.

Evolving Wireless Communications: Addressing the Challenges and Expectations of the Future

The wireless-access networks of today will have to evolve in several ways in order to address the challenges and expectations of the future. New technology components will be introduced as part of the evolution of current wireless-access technologies, such as high-speed packet access (HSPA) and long-term evolution (LTE). However, additional components may also constitute future new wireless-access technologies, which may complement the evolved technologies. Examples of such new technology components are new ways of accessing spectrum and substantially higher frequency ranges, the introduction of massive antenna configurations, direct device-to-device communication, and ultradense deployments.

Waveform and Numerology to Support 5G Services and Requirements

The standardization of the next generation 5G radio access technology has just started in 3GPP with the ambition of making it commercially available by 2020. There are a number of features that are unique for 5G radio access compared to the previous generations such as a wide range of carrier frequencies and deployment options, diverse use cases with very different user requirements, small-size base stations, self-backhaul, massive MIMO, and large channel bandwidths. In this article, we propose a flexible physical layer for the NR to meet the 5G requirements. A symmetric physical layer design with OFDM is proposed for all link types, including uplink, downlink, device-to-device, and backhaul. A scalable OFDM waveform is proposed to handle the wide range of carrier frequencies and deployments.

Improved Data-Aided Channel Estimation in LTE PUCCH Using a Tensor Modeling Approach

NA In 3rd. Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, when no resources has been assigned in the uplink to a given user, the control information associated with Layers 1 and 2 in the protocol stack is conveyed back to the LTE base station (also known as eNodeB) through the so-called Physical Uplink Control Channel (PUCCH). In this work we consider the Format 2 of LTE PUCCH which conveys information about the channel status. At the eNodeB, conventional receivers generally resort to reference signals (RS), or pilot symbols, to perform channel estimation prior to symbol detection. In this paper, we propose a tensor modeling approach for a Data-Aided (DA) channel estimation in PUCCH. First, we formulate the practical channel estimation problem in PUCCH using the Parallel Factor (PARAFAC) tensor model. Based in this model, we resort to the Alternating Least Squares (ALS) algorithm as a DA-based channel estimator. Contrary to conventional RS-based channel estimation operating only on reference signals, the proposed algorithm also simultaneously exploits the energy of the data symbols of all the users, which is contained in PUCCH slots in order to iteratively estimate the user channel coefficients. As will be shown in our simulation results, improved channel estimation accuracy is obtained.

Control Channel Design Trade-Offs for Ultra-Reliable and Low-Latency Communication System

Future generation of wireless networks, i.e. 5G, is envisioned to support several new use-cases demanding transmission reliability and latency that cannot be achieved by the current cellular networks such as long-term evolution (LTE). This paper looks at different design aspects of the control channel(s) to support ultra-reliable low-latency communication considering factory automation as an example scenario. In particular, we show that a fairly balanced design for both the uplink and the downlink control channels can be made given an appropriate selection of modulation, coding, diversity scheme, and time/frequency resources. By means of link-level simulations, we also show that the proposed control channel design supports a block-error rate of 10-9 under Rayleigh fading conditions at a signal-to-interference-plus-noise ratio comparable to that supported by current 4G systems (e.g. LTE). Furthermore, a radio frame structure is proposed to support the user plane end-to-end latency of 1 ms.

A time-domain equalizer minimizing intersymbol and intercarrier interference in DMT systems

Discrete multitone modulation allows for a simple receiver structure if the impulse response of the communication channel is shorter than the cyclic prefix. In ADSL, a time-domain equalizer (TEQ) is used to fulfil this requirement. Without a TEQ, unwanted intercarrier interference (ICI) and intersymbol interference (ISI) occur. In this paper, quadratic forms are developed to calculate the contributions of ICI and ISI to the desired signal. Based on these expressions, a new method for calculating the TEQ coefficients, which minimizes the effects of ICI, ISI, and additive noise, is derived. Simulations in the context of ADSL compare the performance of this new algorithm with one that is state of the art.

Semi-Blind Multi-User Detection for LTE PUCCH

In Long Term Evolution (LTE) specification, physical uplink control channel (PUCCH) consists of two basic transmission formats, i.e. formats 1a/1b and format 2, carrying some control signals fed back to eNodeB, e.g. ACK/NACK related to downlink data transmission blocks and downlink channel quality indicator (CQI). At eNodeB, conventional receiver detection algorithm is to do coherent data detection by utilizing reference signals (RS) based channel estimation, also called non-blind algorithm, whose detection performance is greatly limited by RS density and data coding rate. In this paper, a semi-blind algorithm is introduced to improve channel estimation accuracy by also using data energy besides RS energy at a cost of a higher computational complexity. The analyzes is done for both formats 1a/1b and format 2. Simulation results show that semi-blind algorithms efficiently improve the performance of format 2 because format 2 has lower RS density and higher coding rate than formats 1a/1b.

A new multi-user receiver for PUCCH LTE format 1

In 3rd. Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, when no resources has been assigned in the uplink to a given UE (User Equipment), the ACK/NACK associated with the received packets are conveyed back to the LTE base station through the so-called Physical Uplink Control Channel (PUCCH). In PUCCH, the data streams transmitted by multiple UEs are multiplexed in the frequency-domain with the aid of spreading codes. However, in multi-cell scenarios, the presence of Inter-Cell Interference (ICI) arising from the lack of code orthogonality severely limits receiver performance. In this paper, we propose a new multi-user receiver for PUCCH LTE operating in a cell-cooperative setting. Using the fact that the received signal in PUCCH signaling follows a constrained tensor model, a multiuser receiver based on an iterative joint channel estimation and symbol detection is proposed. The uniqueness conditions of this particular tensor model allows us to derive the maximum number of terminals that can be simultaneously detected at the LTE base station. Simulation results show the remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver.

Numerology and frame structure for 5G radio access

5G radio access technology is envisioned to operate from sub-1 GHz to 100 GHz using a wide range of deployment options and to support diverse services. This paper proposes OFDM numerology and frame structure for 5G radio access. The numerology is proposed keeping in view realistic propagation channel measurements, mobility, effect of phase noise, and implementation complexity. The frame structure is proposed for both FDD and TDD. The proposed frame structure is flexible, scalable, and fulfills low latency requirements.

A Multi-User Receiver for PUCCH LTE FORMAT 1 in Non-Cooperative Multi-Cell Architectures

In this paper, we propose a new multi-user receiver processing for PUCCH LTE that counteracts the ICI in a non-cooperative multi-cell architecture. Using the fact that the received signal in PUCCH signaling follows a constrained tensor model, a multi-user receiver based on an iterative joint channel/code estimation and symbol detection is proposed. The interest in such a challenging setting relies on the overhead reduction among neighboring cells. Simulation results show remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver under the same conditions. We also show a performance comparison with the cooperative version of such a tensor receiver.