Unrepeated fiber transmissions over hundreds of kilometers span with advanced modulation formats and DSP-based coherent detection schemes are considered as a potential candidate to meet the distance and capacity requirements in certain application scenarios where render amplification sites between terminals are impractical due to geographic, commercial or security constrains [1]. Distributed Raman fiber amplifier (DFRA) ensuring a relatively constant power distribution of the optical signals along links can effectively improve the system OSNR and fiber nonlinearity tolerance, therefore is widely adopted in unrepeated transmission solutions. To date, unrepeated transmissions of 30 Gbaud DP-QPSK over 444 km [2], single and dual carrier 28 Gbaud DP-16QAM over 240 km [3, 4] have been demonstrated by using Raman amplification with large effective area fibers (LEAF). In this paper we report on a systematic experimental characterization of both the amplitude and phase impairments of the received signal induced by a bidirectional Raman pump at 1455 nm with an evaluation of the coherent transmission performances of a 28 Gbaud DP-16QAM signal in a standard single mode fiber (SSMF). The Raman induced amplitude and phase noise on the received 1550 nm signal is directly measured and the discussions around the operational rules and limitations are presented considering the inter-relation between pump power, signal OSNR and induced noise. Furthermore, performances of different carrier phase recovery algorithms, including decision-directed phase-locked-loop (DDPLL) [5], blind phase search (BPS) [6] and a two-stage QPSK partitioning [7] with variable filtering implementations in the DSP routine are investigated taking into account the specific noise profile of the received signal.