Adrian Langowski

Time and frequency synchronisation in 4G OFDM systems

This paper presents a complete synchronisation scheme of a baseband OFDM receiver for the currently designed 4G mobile communication system. Since the OFDM transmission is vulnerable to time and frequency offsets, accurate estimation of these parameters is one of the most important tasks of the OFDM receiver. In this paper, the design of a single OFDM synchronisation pilot symbol is introduced. The pilot is used for coarse timing offset and fractional frequency offset estimation. However, it can be applied for fine timing synchronisation and integer frequency offset estimation algorithms as well. A new timing metric that improves the performance of the coarse timing synchronisation is presented. Time domain synchronisation is completed after receiving this single OFDM pilot symbol. During the tracking phase, carrier frequency and sampling frequency offsets are tracked and corrected by means of the nondata-aided algorithm developed by the author. The proposed concept was tested by means of computer simulations, where the OFDM signal was transmitted over a multipath Rayleigh fading channel characterised by the WINNER channel models with Doppler shift and additive white Gaussian noise.

Block-Wise PAPR Minimization Algorithm in MIMO STBC V2V Transmission

In this paper we present an efficient method of peak- to-average power ratio (PAPR) minimization in the space-time block coded (STBC) MIMO orthogonal frequency division multiplexing (OFDM) transmission. The developed system is based on 802.11p standard designed for the communication between vehicles and between vehicles and infrastructure. The presented algorithm belongs to the family of selective mapping (SLM) methods. Since SLM algorithms require that side information is transmitted to the receiver, in the proposed solution pilot tones are used for this purpose.

Throughput enhancement for the 802.11p communication

One of the most important parts of the vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication is reliable transmission that allows the achievement of good throughput in the system. In terms of high system throughput, two issues need to be taken into consideration. First, accurate estimation that is crucial for the successful application of equalization and demodulation, since V2X channel characteristics are very time-varying. Second, properly chosen channel coding. This paper presents effective channel estimation that requires only a slight modification to the 802.11p standard pilot scheme and also presents the impact of turbo coding on system throughput.

A novel blockwise PAPR minimization algorithm for connected vehicles

In this paper we present a novel algorithm which minimizes peak-to-average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) signal used in IEEE 802.11p like transmission. The proposed algorithm is an extension of the widely known selected mapping (SLM) algorithm. Its novelty relies on performing PAPR minimization jointly in blocks of a few OFDM symbols and transmitting on side information usually required by the SML algorithm on pilot positions. Simulation results prove the usefulness of the proposed algorithm.1.

Fast and accurate OFDM time and frequency synchronisation

This paper presents a complete synchronization scheme of a baseband OFDM receiver for currently designed mobile communication system to be proposed as a candidate for 4G mobile communication system. The structure of a synchronisation pilot symbol is proposed. The following functional parts of the receiver are presented: coarse and fine symbol timing synchronization and coarse and fine frequency synchronization. New timing metric improving the performance of the coarse timing synchronisation is proposed. The synchronisation is completed after receiving only one OFDM pilot symbol. Simulations proving the concept were performed transmitting the signal over multipath, Rayleigh fading channel characterised by the WINNER channel models with Doppler shift and additive white noise.

A novel pilot scheme for 5G downlink transmission

The paper considers the structure of pilots for downlink transmission in a future 5G radio access system. Based on the OFDM signal parameters proposed for the 5G system by Mogensen et al., we suggest to apply a periodical filtered CAZAC sequence in the time domain. We demonstrate the low computational complexity of channel impulse response estimation and its better accuracy if it is based on our time domain pilot sequence as compared with the pilot sequence placed in the frequency domain and based on Zadoff-Chu sequences. The presented link level simulations show the superiority of our pilot design proposal with respect to frequency domain pilot sequences.

Increasing Uplink Data Rates in HSPA by Modified Mapping of OVSF Codes

The paper is devoted to the studies on modifications of mapping of the OVSF channelization codes onto the data and control channels in HSUPA, aiming at increasing the uplink data rates. Appropriate selection of mapping can result in a link throughput gain of up to 28% as compared with the standard HSUPA transmission. An intensive HSUPA link level simulation campaign has been performed to investigate many possible mappings, to optimize the ratios of traffic to pilot channel powers and to measure parameters of the transmitted signal such as the peak-to-average power ratio and the cubic metric. The most important and representative results are summarized in this paper.